Fuel Consumption Unit Converter

Quick Start: Fuel Consumption Conversions

Convert between fuel efficiency units instantly. Our free calculator handles MPG (US/UK), L/100km, km/L, and helps compare vehicle fuel economy worldwide.

Most Popular Conversions:

• MPG (US) to L/100km - US to metric
• L/100km to MPG (US) - Metric to US
• MPG (UK) to L/100km - UK to metric
• km/L to MPG (US) - Metric alternative
• MPG (US) to MPG (UK) - US to UK comparison
• MPG (US) to km/L - US to international
• km/L to L/100km - Inverse relationship

Why Fuel Consumption Conversion Matters

Understanding fuel efficiency across different measurement systems is essential:

1. International Vehicle Comparison

Compare cars from different markets accurately. A 35 MPG (US) car equals 42 MPG (UK) or 6.7 L/100km—knowing this helps evaluate import vehicles, rental cars abroad, and international specifications.

2. Travel Planning & Budgeting

Calculate fuel costs when traveling internationally. Convert between local units to estimate trip expenses, plan refueling stops, and budget accurately for road trips.

3. Vehicle Purchase Decisions

Evaluate real fuel economy when shopping for cars. Compare efficiency ratings across manufacturers and countries to make informed purchase decisions and calculate long-term ownership costs.

4. Environmental Impact Assessment

Understand your vehicle's carbon footprint regardless of how efficiency is reported. Convert to common units to compare environmental impact and track emissions reductions.

5. Fleet Management & Business

Manage company vehicles across different regions, calculate fuel budgets, track efficiency improvements, and optimize fleet operations with standardized metrics.

Common Fuel Consumption Units Explained

Distance per Volume Units (Higher = Better)

Miles per Gallon - US (MPG US) - Miles traveled per US gallon (3.785 liters). Standard in United States. Higher values indicate better fuel efficiency.

Miles per Gallon - UK (MPG UK) - Miles traveled per Imperial gallon (4.546 liters). Used in United Kingdom. About 20% higher than US MPG for same vehicle due to larger gallon.

Kilometers per Liter (km/L) - Kilometers traveled per liter. Common in Asia, Latin America, and as alternative metric. Easy to compare with L/100km.

Miles per Liter (MPL) - Miles traveled per liter. Less common, mainly for conversions between imperial and metric systems.

Volume per Distance Units (Lower = Better)

Liters per 100 Kilometers (L/100km) - Liters consumed to travel 100 kilometers. Standard in Europe, Canada, Australia, much of world. Lower values indicate better fuel efficiency.

Gallons per 100 Miles (gal/100mi) - Rarely used, but sometimes appears in US contexts. Lower is better.

Key Understanding: Inverse Relationship

MPG and L/100km have an inverse relationship:

• High MPG (35 MPG) = Low L/100km (6.7 L/100km) = Good efficiency
• Low MPG (15 MPG) = High L/100km (15.7 L/100km) = Poor efficiency

Fuel Consumption Quick Reference Tables

MPG (US) to L/100km Conversion

MPG (US)	L/100km	Efficiency
10 MPG	23.5 L/100km	Very poor (large SUV, truck)
15 MPG	15.7 L/100km	Poor (older SUV, performance car)
20 MPG	11.8 L/100km	Below average (SUV, truck)
25 MPG	9.4 L/100km	Average (sedan, crossover)
30 MPG	7.8 L/100km	Good (efficient sedan)
35 MPG	6.7 L/100km	Very good (hybrid, small car)
40 MPG	5.9 L/100km	Excellent (hybrid, diesel)
50 MPG	4.7 L/100km	Outstanding (hybrid)
60 MPG	3.9 L/100km	Exceptional (plug-in hybrid)

MPG (UK) to L/100km Conversion

MPG (UK)	L/100km	MPG (US) Equivalent
20 MPG	14.1 L/100km	16.7 MPG (US)
30 MPG	9.4 L/100km	25.0 MPG (US)
40 MPG	7.1 L/100km	33.3 MPG (US)
50 MPG	5.6 L/100km	41.6 MPG (US)
60 MPG	4.7 L/100km	50.0 MPG (US)
70 MPG	4.0 L/100km	58.3 MPG (US)

km/L to Other Units

km/L	MPG (US)	L/100km	Efficiency
5 km/L	11.8 MPG	20 L/100km	Poor
8 km/L	18.8 MPG	12.5 L/100km	Below average
10 km/L	23.5 MPG	10 L/100km	Average
12 km/L	28.2 MPG	8.3 L/100km	Good
15 km/L	35.3 MPG	6.7 L/100km	Very good
20 km/L	47.0 MPG	5 L/100km	Excellent
25 km/L	58.8 MPG	4 L/100km	Outstanding

Typical Vehicle Fuel Economy by Type

Vehicle Type	MPG (US)	L/100km	km/L
Large SUV/Truck	12-18 MPG	13-20 L/100km	5-8 km/L
Mid-size SUV	18-25 MPG	9-13 L/100km	8-11 km/L
Sedan (average)	25-32 MPG	7-9 L/100km	11-14 km/L
Compact car	30-38 MPG	6-8 L/100km	13-16 km/L
Hybrid	40-58 MPG	4-6 L/100km	17-25 km/L
Plug-in hybrid (gas)	30-50 MPG	5-8 L/100km	13-21 km/L
Performance car	15-22 MPG	11-16 L/100km	6-9 km/L

Practical Fuel Consumption Conversion Examples

International Travel & Vehicle Rental

Example 1: European Rental Car Comparison

• Problem: Rental car advertised as 5.5 L/100km. What's that in MPG (US)?
• Solution: 235.21 ÷ 5.5 = 42.8 MPG (US)
• Use case: Understanding European car specs, comparing rental options

Example 2: US Car in Canada

• Problem: Your US car gets 28 MPG. Canadian gas stations show L/100km. What to expect?
• Solution: 235.21 ÷ 28 = 8.4 L/100km
• Use case: Travel planning, fuel budget estimation

Example 3: UK to US Conversion

• Problem: British car spec sheet shows 52 MPG (UK). What's the US equivalent?
• Solution: 52 ÷ 1.201 = 43.3 MPG (US)
  • Or: 282.48 ÷ 52 = 5.4 L/100km, then 235.21 ÷ 5.4 = 43.6 MPG (US)
• Use case: Importing vehicles, comparing international models

Fuel Cost Calculations

Example 4: Trip Fuel Cost Estimation

• Problem: 500-mile trip, car gets 30 MPG (US), gas costs $3.50/gallon. Total fuel cost?
• Solution:
  • Gallons needed: 500 miles ÷ 30 MPG = 16.67 gallons
  • Cost: 16.67 × $3.50 = $58.33
• Use case: Road trip budgeting, vacation planning

Example 5: Metric Fuel Cost Calculation

• Problem: 800 km trip, car uses 7 L/100km, fuel costs €1.60/L. Total cost?
• Solution:
  • Fuel needed: (800 km ÷ 100) × 7 L = 56 L
  • Cost: 56 × €1.60 = €89.60
• Use case: European travel budgeting

Example 6: Annual Fuel Cost Comparison

• Problem: Drive 15,000 miles/year. Compare 25 MPG SUV vs 40 MPG hybrid at $3.75/gal.
• Solution:
  • SUV: (15,000 ÷ 25) × $3.75 = 600 gal × $3.75 = $2,250/year
  • Hybrid: (15,000 ÷ 40) × $3.75 = 375 gal × $3.75 = $1,406/year
  • Savings: $844/year with hybrid
• Use case: Vehicle purchase decision, cost of ownership

Vehicle Purchase & Comparison

Example 7: Real-World vs EPA Ratings

• Problem: Car rated 35 MPG (combined), but you're getting 28 MPG. What's the L/100km difference?
• Solution:
  • Rated: 235.21 ÷ 35 = 6.7 L/100km
  • Actual: 235.21 ÷ 28 = 8.4 L/100km
  • Difference: 1.7 L/100km higher (25% more fuel than rated)
• Use case: Setting realistic expectations, troubleshooting efficiency

Example 8: Hybrid vs Gas Comparison

• Problem: Compare Honda Civic (33 MPG) vs Civic Hybrid (48 MPG) for 12,000 mi/year, $3.50/gal.
• Solution:
  • Gas: (12,000 ÷ 33) × $3.50 = $1,273/year
  • Hybrid: (12,000 ÷ 48) × $3.50 = $875/year
  • Annual savings: $398
  • Hybrid premium payback: If hybrid costs $3,000 more, payback in 7.5 years
• Use case: Hybrid purchase justification

Example 9: Diesel vs Gasoline

• Problem: Diesel car: 45 MPG, $4.00/gal diesel. Gas car: 32 MPG, $3.50/gal gas. Which is cheaper for 10,000 miles?
• Solution:
  • Diesel: (10,000 ÷ 45) × $4.00 = $889
  • Gas: (10,000 ÷ 32) × $3.50 = $1,094
  • Diesel saves $205 over 10,000 miles
• Use case: Fuel type comparison, TCO analysis

Fleet Management & Business

Example 10: Fleet Efficiency Improvement

• Problem: Company has 20 vans averaging 18 MPG, driving 25,000 mi/year each. Upgrading to 25 MPG vans. Annual fuel savings at $3.80/gal?
• Solution:
  • Old fleet: 20 × (25,000 ÷ 18) × $3.80 = $105,556/year
  • New fleet: 20 × (25,000 ÷ 25) × $3.80 = $76,000/year
  • Annual savings: $29,556
• Use case: Fleet upgrade ROI calculation

Example 11: International Fleet Comparison

• Problem: Standardize efficiency reporting for global fleet: US vehicles in MPG, European in L/100km.
• Solution: Convert all to L/100km for consistent comparison:
  • US van (15 MPG): 235.21 ÷ 15 = 15.7 L/100km
  • EU van (8.5 L/100km): 8.5 L/100km
  • EU van is 46% more efficient
• Use case: Global fleet optimization

Environmental Impact

Example 12: CO2 Emissions Calculation

• Problem: Car gets 30 MPG, drive 12,000 mi/year. Approximate CO2 emissions?
• Solution:
  • Fuel used: 12,000 ÷ 30 = 400 gallons
  • CO2 per gallon: ~8.89 kg (gasoline combustion)
  • Annual CO2: 400 × 8.89 = 3,556 kg (3.56 tonnes)
• Use case: Carbon footprint calculation, environmental awareness

Example 13: Efficiency Improvement Impact

• Problem: Improving from 22 MPG to 30 MPG for 15,000 mi/year. CO2 reduction?
• Solution:
  • Old: (15,000 ÷ 22) × 8.89 kg = 6,059 kg CO2
  • New: (15,000 ÷ 30) × 8.89 kg = 4,445 kg CO2
  • Reduction: 1,614 kg CO2/year (26.6% less)
• Use case: Environmental impact of vehicle choice

Common Fuel Consumption Conversion Mistakes

1. Confusing US and UK Gallons

Mistake: Using MPG (UK) numbers as if they were MPG (US).

Example: Seeing a car rated at 50 MPG (UK) and assuming it gets 50 MPG (US).

Correct approach: UK gallons are 20% larger, so UK MPG is always higher.

• 50 MPG (UK) = 41.6 MPG (US)
• Conversion: MPG (US) = MPG (UK) ÷ 1.201

Why it matters: This 20% difference significantly affects fuel cost estimates and vehicle comparisons. A car appearing highly efficient in UK terms may be merely average in US terms.

Quick tip: UK MPG numbers look better but represent the same efficiency. Always check which gallon is being used.

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2. Forgetting the Inverse Relationship (MPG vs L/100km)

Mistake: Thinking that doubling MPG halves fuel consumption proportionally.

Example: Believing going from 20 MPG to 40 MPG saves the same fuel as going from 40 MPG to 60 MPG.

Correct understanding:

• 20 to 40 MPG: 11.8 L/100km to 5.9 L/100km = 5.9 L/100km saved
• 40 to 60 MPG: 5.9 L/100km to 3.9 L/100km = 2.0 L/100km saved

Why it matters: Fuel savings are non-linear with MPG. Upgrading from 15 to 20 MPG saves MORE fuel than upgrading from 40 to 45 MPG, even though both are 5 MPG improvements.

Quick tip: Use L/100km for accurate savings comparisons—the differences are linear and more intuitive.

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3. Not Accounting for Real-World vs EPA Ratings

Mistake: Expecting actual fuel economy to match EPA/NEDC/WLTP ratings.

Example: Budgeting fuel costs based on EPA combined 35 MPG, but actually getting 28 MPG.

Correct approach: Real-world fuel economy is typically 15-30% worse than official ratings.

• EPA 35 MPG → Real-world 25-30 MPG typical
• Factors: Traffic, weather, terrain, driving style, A/C use, load

Why it matters: Fuel cost estimates and range calculations will be significantly off if using official ratings alone.

Quick tip: Reduce EPA estimates by 20-25% for realistic real-world expectations. Check owner forums for actual user-reported MPG.

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4. Mixing Distance Units (Miles vs Kilometers)

Mistake: Using kilometers with MPG or miles with L/100km in calculations.

Example: Calculating trip fuel for 500 km using 30 MPG as if it were km/L.

Correct approach: Always match distance units with fuel efficiency units.

• MPG: Use with miles
• km/L: Use with kilometers
• L/100km: Use with kilometers

Example calculation:

• 500 km trip, 30 MPG car
• Convert: 30 MPG = 12.75 km/L
• Fuel: 500 km ÷ 12.75 km/L = 39.2 liters

Why it matters: Mixing units causes massive calculation errors, leading to running out of fuel or severe budget miscalculations.

Quick tip: Always convert everything to the same system (all metric or all imperial) before calculating.

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5. Ignoring City vs Highway Differences

Mistake: Using combined/average MPG for specific driving conditions.

Example: Planning highway road trip using combined 30 MPG, when highway is 36 MPG.

Correct approach: Use appropriate rating for your driving:

• City: Stop-and-go, lower efficiency (typically 20-30% worse)
• Highway: Steady speed, better efficiency
• Combined: Weighted average (~55% city, 45% highway)

Typical spread:

• City: 25 MPG
• Highway: 35 MPG
• Combined: 29 MPG

Why it matters: Highway trips will use significantly less fuel than city driving. Using wrong figure can cause 20-40% error in fuel estimates.

Quick tip: For road trips, use highway rating. For daily commuting in traffic, use city rating or even reduce it by 10%.

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6. Not Accounting for Fuel Type Differences

Mistake: Comparing diesel and gasoline efficiency without considering energy content differences.

Example: Thinking 45 MPG diesel is directly comparable to 45 MPG gasoline in environmental impact.

Correct understanding: Diesel has ~12% more energy per gallon than gasoline.

• 45 MPG diesel ≈ 50 MPG gasoline equivalent (energy basis)
• CO2 emissions: Diesel produces ~15% more CO2 per gallon

Why it matters: Direct MPG comparisons between fuel types don't reflect true energy efficiency or emissions. Diesel cars often show better MPG but not proportionally better emissions.

Quick tip: For environmental comparisons, look at CO2 g/km or g/mile ratings rather than just MPG.

Frequently Asked Questions (FAQs)

What's the difference between MPG (US) and MPG (UK)?

The difference is in the size of the gallon used:

US Gallon:

• Volume: 3.785 liters (231 cubic inches)
• Used in: United States
• Smaller gallon = lower MPG numbers

Imperial Gallon (UK):

• Volume: 4.546 liters (277.4 cubic inches)
• Used in: United Kingdom, some Commonwealth countries
• 20% larger than US gallon = higher MPG numbers

Conversion: 1 MPG (UK) = 1.201 MPG (US)

Examples:

• 30 MPG (US) = 36 MPG (UK)
• 40 MPG (UK) = 33.3 MPG (US)
• 50 MPG (UK) = 41.6 MPG (US)

Why it matters: A car with "50 MPG" in UK literature would only achieve 41.6 MPG in US terms. When comparing international vehicles, always verify which gallon is used.

Quick check: UK MPG numbers are always about 20% higher than US MPG for the same vehicle. If you see surprisingly high MPG, it's likely UK gallons.

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Is higher or lower fuel consumption better?

It depends on which unit you're using:

Higher is better:

• MPG (US) - More miles per gallon = better
• MPG (UK) - More miles per gallon = better
• km/L - More kilometers per liter = better
• MPL - More miles per liter = better

Lower is better:

• L/100km - Fewer liters per 100 km = better
• gal/100mi - Fewer gallons per 100 miles = better

Examples of good efficiency:

• MPG: 35+ MPG (US), 42+ MPG (UK)
• L/100km: Below 7 L/100km
• km/L: Above 14 km/L

Examples of poor efficiency:

• MPG: Below 20 MPG (US), below 24 MPG (UK)
• L/100km: Above 12 L/100km
• km/L: Below 8 km/L

Why the confusion: MPG measures "distance per fuel" (higher = more efficient), while L/100km measures "fuel per distance" (lower = less fuel needed = more efficient). They're inverse relationships.

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How do I convert MPG (US) to L/100km?

Use the formula: L/100km = 235.21 ÷ MPG (US)

Step-by-step:

1. Take the constant 235.21
2. Divide by your MPG (US) value
3. Result is L/100km

Common conversions:

• 15 MPG (US) = 235.21 ÷ 15 = 15.7 L/100km
• 20 MPG (US) = 235.21 ÷ 20 = 11.8 L/100km
• 25 MPG (US) = 235.21 ÷ 25 = 9.4 L/100km
• 30 MPG (US) = 235.21 ÷ 30 = 7.8 L/100km
• 35 MPG (US) = 235.21 ÷ 35 = 6.7 L/100km
• 40 MPG (US) = 235.21 ÷ 40 = 5.9 L/100km
• 50 MPG (US) = 235.21 ÷ 50 = 4.7 L/100km

Reverse (L/100km to MPG US): MPG (US) = 235.21 ÷ L/100km

Where 235.21 comes from:

• 100 km = 62.137 miles
• 1 US gallon = 3.78541 liters
• 100 ÷ 3.78541 × 62.137 = 235.21

Quick mental estimate: Divide 240 by MPG for rough L/100km.

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How do I convert km/L to L/100km?

These have a simple inverse relationship: L/100km = 100 ÷ km/L

Formula: L/100km = 100 ÷ km/L or km/L = 100 ÷ L/100km

Examples:

• 5 km/L = 100 ÷ 5 = 20 L/100km
• 8 km/L = 100 ÷ 8 = 12.5 L/100km
• 10 km/L = 100 ÷ 10 = 10 L/100km
• 12 km/L = 100 ÷ 12 = 8.3 L/100km
• 15 km/L = 100 ÷ 15 = 6.7 L/100km
• 20 km/L = 100 ÷ 20 = 5 L/100km
• 25 km/L = 100 ÷ 25 = 4 L/100km

Reverse examples:

• 5 L/100km = 100 ÷ 5 = 20 km/L
• 7 L/100km = 100 ÷ 7 = 14.3 km/L
• 10 L/100km = 100 ÷ 10 = 10 km/L

Why this works: km/L tells you how far you go per liter. L/100km tells you how many liters you use per 100 km. They're exact inverses scaled to 100.

Mental math trick: Easy to calculate mentally—just divide 100 by the number.

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Why are real-world MPG numbers different from EPA ratings?

EPA (and other official) tests are standardized laboratory tests that don't fully reflect real-world driving conditions.

Factors making real-world MPG lower:

1. Driving conditions:

• Heavy traffic (stop-and-go)
• Aggressive acceleration/braking
• High speeds (above 65 mph/105 km/h)
• Hilly terrain
• Short trips (cold engine)

2. Environmental factors:

• Extreme temperatures (heat or cold)
• Headwinds
• Use of air conditioning/heating
• Altitude changes

3. Vehicle factors:

• Additional weight/cargo
• Roof racks or carriers
• Under-inflated tires
• Poor maintenance
• Lower-grade fuel

4. Test procedure limitations:

• EPA tests are standardized cycles
• Performed in controlled laboratory
• Limited temperature range
• No accessories (A/C, lights, etc.)
• Optimal tire pressure
• Break-in vehicles

Typical differences:

• EPA highway: -15 to -20% in real world
• EPA city: -20 to -30% in real world
• EPA combined: -20 to -25% in real world

Example:

• EPA combined: 30 MPG
• Real-world typical: 24-27 MPG
• Real-world worst case: 20-23 MPG

Newer standards (post-2008) are more realistic than older EPA tests, but still optimistic.

Best resource: Check owner-reported MPG on sites like Fuelly.com or vehicle-specific forums for realistic expectations.

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How much does improving MPG save on fuel costs?

Savings depend on miles driven, current MPG, new MPG, and fuel price.

Formula: Annual Savings = (Miles/Year) × Fuel Price × (1/Old MPG - 1/New MPG)

Example 1: Moderate improvement

• Scenario: 15,000 mi/year, $3.75/gal, upgrading 25 MPG → 32 MPG
• Calculation:
  • Old cost: (15,000 ÷ 25) × $3.75 = $2,250/year
  • New cost: (15,000 ÷ 32) × $3.75 = $1,758/year
  • Annual savings: $492

Example 2: Large improvement

• Scenario: 12,000 mi/year, $3.50/gal, upgrading 18 MPG → 35 MPG
• Calculation:
  • Old cost: (12,000 ÷ 18) × $3.50 = $2,333/year
  • New cost: (12,000 ÷ 35) × $3.50 = $1,200/year
  • Annual savings: $1,133

Example 3: Small improvement

• Scenario: 10,000 mi/year, $4.00/gal, upgrading 35 MPG → 40 MPG
• Calculation:
  • Old cost: (10,000 ÷ 35) × $4.00 = $1,143/year
  • New cost: (10,000 ÷ 40) × $4.00 = $1,000/year
  • Annual savings: $143

Key insight: Improvements at lower MPG save more money than improvements at higher MPG, even for the same MPG increase:

• 15 → 20 MPG saves more than 40 → 45 MPG
• 20 → 25 MPG saves more than 35 → 40 MPG

Payback period: Divide hybrid/efficient vehicle premium by annual savings to find payback years.

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What is good fuel economy for different vehicle types?

"Good" fuel economy varies by vehicle size and purpose:

Small Cars & Sedans:

• Poor: Below 25 MPG (US) / 9.4 L/100km
• Average: 28-35 MPG / 6.7-8.4 L/100km
• Good: 35-42 MPG / 5.6-6.7 L/100km
• Excellent: Above 45 MPG / 5.2 L/100km

Mid-Size Sedans:

• Poor: Below 22 MPG / 10.7 L/100km
• Average: 24-30 MPG / 7.8-9.8 L/100km
• Good: 30-37 MPG / 6.4-7.8 L/100km
• Excellent: Above 40 MPG / 5.9 L/100km

SUVs & Crossovers:

• Poor: Below 18 MPG / 13 L/100km
• Average: 20-26 MPG / 9-11.8 L/100km
• Good: 26-32 MPG / 7.4-9 L/100km
• Excellent: Above 35 MPG / 6.7 L/100km

Pickup Trucks:

• Poor: Below 15 MPG / 15.7 L/100km
• Average: 16-22 MPG / 10.7-14.7 L/100km
• Good: 22-28 MPG / 8.4-10.7 L/100km
• Excellent: Above 30 MPG / 7.8 L/100km

Hybrids:

• Average: 40-50 MPG / 4.7-5.9 L/100km
• Good: 50-58 MPG / 4.1-4.7 L/100km
• Excellent: Above 58 MPG / 4.1 L/100km

Performance Cars:

• Poor: Below 15 MPG / 15.7 L/100km
• Average: 16-22 MPG / 10.7-14.7 L/100km
• Good: 22-28 MPG / 8.4-10.7 L/100km (for performance category)

Context matters: A pickup truck getting 25 MPG is excellent for its class, while a sedan getting 25 MPG is below average.

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How do I calculate fuel cost for a trip?

Formula: Fuel Cost = (Distance ÷ Fuel Economy) × Fuel Price

Step-by-step process:

1. Determine distance:

• Example: 750 miles (or 1,200 km)

2. Know your fuel economy:

• Example: 28 MPG (US) or 8.4 L/100km

3. Find current fuel price:

• Example: $3.65/gallon or €1.55/liter

4. Calculate fuel needed:

• US units: 750 miles ÷ 28 MPG = 26.79 gallons
• Metric: (1,200 km ÷ 100) × 8.4 L/100km = 100.8 liters

5. Calculate total cost:

• US: 26.79 gal × $3.65 = $97.78
• Metric: 100.8 L × €1.55 = €156.24

Additional examples:

Road trip (MPG):

• 1,500 miles, 32 MPG, $3.50/gal
• (1,500 ÷ 32) × $3.50 = $164.06

European trip (L/100km):

• 800 km, 6.5 L/100km, €1.70/L
• (800 ÷ 100) × 6.5 × €1.70 = €88.40

Round trip:

• 450 miles each way = 900 miles total
• 25 MPG, $3.80/gal
• (900 ÷ 25) × $3.80 = $136.80

Buffer tip: Add 10-15% for detours, traffic, and fuel price variations along route.

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What's the most fuel-efficient driving speed?

Most vehicles achieve peak fuel efficiency at 40-60 mph (65-95 km/h), typically around 50-55 mph (80-90 km/h).

Fuel economy by speed (typical sedan):

• 30 mph (48 km/h): ~33 MPG / 7.1 L/100km (good, but slow)
• 40 mph (64 km/h): ~36 MPG / 6.5 L/100km (excellent)
• 50 mph (80 km/h): ~38 MPG / 6.2 L/100km (optimal)
• 60 mph (97 km/h): ~36 MPG / 6.5 L/100km (very good)
• 70 mph (113 km/h): ~31 MPG / 7.6 L/100km (good)
• 80 mph (129 km/h): ~25 MPG / 9.4 L/100km (poor)
• 90 mph (145 km/h): ~20 MPG / 11.8 L/100km (very poor)

Why efficiency drops at high speeds:

• Aerodynamic drag increases exponentially (proportional to speed²)
• Engine works harder to maintain speed
• Wind resistance becomes dominant factor

Impact of speeding:

• Every 5 mph above 60 mph = ~7-10% worse fuel economy
• Driving 80 mph vs 65 mph = ~20-25% more fuel
• For 500-mile trip: Could cost $15-30 more in fuel

Other factors:

• Lower speeds in stop-and-go: Efficiency drops due to acceleration
• Optimal cruise: Steady speed without braking/acceleration
• Drafting trucks: Improves efficiency but dangerous

Best practice: On highways, stay at or slightly below speed limit (60-70 mph). Use cruise control for steady speed.

Urban driving: Smooth acceleration and coasting maximize efficiency more than specific speed.

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How much does air conditioning affect fuel economy?

Air conditioning can reduce fuel economy by 5-25%, depending on conditions and usage.

Impact by scenario:

City driving (low speeds):

• A/C impact: 15-25% worse MPG
• Example: 30 MPG → 22-25 MPG
• Reason: Engine working harder at low RPM

Highway driving (high speeds):

• A/C impact: 5-10% worse MPG
• Example: 38 MPG → 34-36 MPG
• Reason: Engine at efficient RPM, A/C load relatively smaller

Extreme heat (95°F+/35°C+):

• A/C impact: 20-30% worse MPG initially
• After cabin cooled: 10-15% worse
• Example: 28 MPG → 19-24 MPG initially

Factors affecting impact:

• Temperature difference (bigger difference = more impact)
• A/C setting (max cold = most impact)
• Recirculation mode (slightly better than fresh air)
• Vehicle size (smaller engines feel it more)

Windows down vs A/C:

Below 40-45 mph:

• Windows down: Better fuel economy
• A/C impact: 15-20% worse

Above 50-55 mph:

• Windows down: Worse (aerodynamic drag)
• A/C: Better choice
• Open windows drag: 10-20% worse at highway speed

Recommendations:

• City: Open windows if tolerable
• Highway: Use A/C, keep windows closed
• Moderate settings: Use eco mode if available, moderate temperature
• Pre-cool: Start A/C while parked if possible (if safe/legal)

Cost example:

• 12,000 mi/year, 25 MPG without A/C, 20 MPG with A/C, $3.50/gal
• No A/C: $1,680/year
• With A/C: $2,100/year
• A/C cost: $420/year extra

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How can I improve my vehicle's fuel economy?

Multiple strategies can improve fuel economy by 10-30% or more:

Driving Habits (10-30% improvement):

1. Smooth acceleration

• Gradual throttle (5-10% improvement)
• Avoid jackrabbit starts
• Accelerate to speed limit steadily

2. Anticipate stops

• Coast to red lights/stops
• Avoid unnecessary braking
• Leave following distance
• Savings: 5-15%

3. Maintain steady speed

• Use cruise control on highways
• Avoid speed fluctuations
• Savings: 5-10%

4. Reduce speed

• Drive 65 mph instead of 75 mph
• Savings: 10-15%

5. Minimize idling

• Turn off engine for stops over 30 seconds
• Savings: 1-5% in city

Vehicle Maintenance (5-15% improvement):

1. Proper tire pressure

• Check monthly, inflate to recommended PSI
• Under-inflation by 10 PSI: 2-3% worse MPG
• Savings: 3-5%

2. Regular maintenance

• Oil changes on schedule
• Clean air filter
• Spark plugs
• Savings: 5-10%

3. Wheel alignment

• Correct alignment reduces drag
• Savings: 1-2%

Weight & Aerodynamics (5-10% improvement):

1. Remove excess weight

• 100 lbs reduces MPG by 1-2%
• Clean out trunk/cargo area

2. Remove roof racks

• Roof racks: 5-10% worse MPG at highway speed
• Cargo box: 10-25% worse
• Remove when not in use

3. Close windows at high speed

• Above 50 mph: Significant drag
• Use A/C instead at highway speed

Combined impact example:

• Starting MPG: 25 MPG
• Smooth driving: +10% = 27.5 MPG
• Proper maintenance: +5% = 28.9 MPG
• Tire pressure: +3% = 29.8 MPG
• Remove 150 lbs: +2% = 30.4 MPG
• Total improvement: 21.6% (5.4 MPG gain)

Cost savings (15,000 mi/year, $3.75/gal):

• 25 MPG: $2,250/year
• 30.4 MPG: $1,850/year
• Annual savings: $400

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Related Converters

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• Length Converter - Distance measurements (miles, kilometers)
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Popular Fuel Consumption Conversion Pairs

Quick access to the most commonly used fuel consumption conversions:

• MPG (US) to L/100km - US to metric
• L/100km to MPG (US) - Metric to US
• MPG (UK) to L/100km - UK to metric
• L/100km to MPG (UK) - Metric to UK
• MPG (US) to MPG (UK) - US to UK
• MPG (UK) to MPG (US) - UK to US
• km/L to MPG (US) - Metric to US
• MPG (US) to km/L - US to metric alt
• km/L to L/100km - Inverse
• L/100km to km/L - Inverse reverse
• MPG (UK) to km/L - UK to metric
• km/L to MPG (UK) - Metric to UK
• MPL to MPG (US) - Liter basis
• MPG (US) to MPL - Gallon to liter
• km/L to MPL - Metric swap
• L/100km to gal/100mi - Inverse units
• gal/100mi to L/100km - Inverse reverse
• MPG (US) to gal/100mi - US inversion
• MPL to km/L - Distance conversion
• MPL to L/100km - Mixed conversion