Energy Unit Converter

Quick Start: Energy Conversions

Convert between 15+ energy units instantly. Perfect for electricity bills (kWh), nutrition (calories), HVAC (BTU), physics, engineering, and scientific calculations.

Most Popular Conversions:

• kWh to Joules - Electricity to SI units
• Calories to Joules - Food energy to physics
• BTU to kWh - HVAC to electrical energy
• Joules to kWh - Physics to utility billing
• Kilocalories to Joules - Food calories to SI

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Understanding Energy Conversions

Energy is the capacity to do work or produce heat. It's measured in various units depending on the application—joules in physics, kilowatt-hours on electricity bills, calories in nutrition, and BTU in heating/cooling systems.

Why Energy Conversion Matters

Electricity Bills & Utilities: Power companies bill in kilowatt-hours (kWh), but appliances may specify energy in joules or watt-hours. Understanding conversions helps calculate costs and consumption.

Nutrition & Food: Food energy is measured in kilocalories (kcal or "Calories" with capital C). Converting to joules helps understand energy content in scientific terms.

HVAC & Climate Control: Air conditioners, heaters, and furnaces use BTU (British Thermal Units) ratings. Converting to kWh or watts helps compare efficiency and operating costs.

Physics & Engineering: The SI unit joule is standard in science. Converting from other units (BTU, calories, kWh) enables proper calculations and comparisons.

Renewable Energy: Solar panels, batteries, and generators specify capacity in kWh or watt-hours. Understanding conversions helps size systems correctly.

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Common Energy Units Explained

SI (Metric) Units

Joule (J) - Base Unit: The fundamental SI unit of energy. 1 Joule = work done by 1 newton of force over 1 meter = 1 kg⋅m²/s². Very small for everyday use, so kilo-, mega-, and giga- prefixes are common.

Kilojoule (kJ): 1,000 joules. Common in nutrition labels outside the US (alongside kcal). Used in chemistry, engineering, and some food labeling.

Megajoule (MJ): 1,000,000 joules (1,000 kJ). Used for large-scale energy measurements, fuel energy content, and industrial processes.

Gigajoule (GJ): 1,000,000,000 joules (1,000 MJ). Natural gas consumption, industrial energy use, large-scale power generation.

Electrical Energy Units

Watt-hour (Wh): Energy consumed by 1 watt of power for 1 hour. 1 Wh = 3,600 joules. Used for battery capacity (laptop batteries, power banks).

Kilowatt-hour (kWh): 1,000 watt-hours = 3,600,000 joules. The standard unit for electricity billing worldwide. Your electric meter measures kWh consumed.

Megawatt-hour (MWh): 1,000 kWh = 3,600,000,000 joules. Industrial electricity consumption, large commercial buildings, power plant output.

Heat & Thermal Energy

Calorie (cal) - Small calorie: Energy needed to raise 1 gram of water by 1°C. 1 cal = 4.184 joules. Used in chemistry and older scientific literature.

Kilocalorie (kcal) - Large Calorie or "food Calorie": 1,000 small calories = 4,184 joules. The "Calorie" on food labels (capital C) is actually 1 kilocalorie. Universal in nutrition.

British Thermal Unit (BTU): Energy needed to raise 1 pound of water by 1°F. 1 BTU ≈ 1,055 joules. Standard in US HVAC industry—air conditioner capacities rated in BTU/hour.

Therm: 100,000 BTU = 105.5 megajoules. Used for natural gas billing in the US. 1 therm ≈ 29.3 kWh.

Imperial / US Units

Foot-pound (ft⋅lb): Energy to lift 1 pound by 1 foot against gravity. 1 ft⋅lb ≈ 1.356 joules. Used in mechanical engineering, ballistics, torque specifications.

Scientific Units

Electronvolt (eV): Extremely small unit for atomic/subatomic energy. 1 eV ≈ 1.602 × 10⁻¹⁹ joules. Used in particle physics, quantum mechanics, semiconductor physics.

Erg: CGS unit of energy. 1 erg = 10⁻⁷ joules. Rarely used today except in astrophysics and legacy scientific literature.

Quad: 1 quadrillion BTU (10¹⁵ BTU). Used for national energy statistics and global energy consumption reporting.

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Conversion Quick Reference

Common Conversions

From	To	Multiply By	Example
kWh	Joules	3,600,000	1 kWh = 3.6 MJ
kWh	BTU	3,412.14	1 kWh = 3,412 BTU
BTU	kWh	0.000293071	10,000 BTU = 2.93 kWh
BTU	Joules	1,055.06	1,000 BTU = 1.055 MJ
kcal	Joules	4,184	500 kcal = 2.092 MJ
kcal	kWh	0.001162	1,000 kcal = 1.162 kWh
Joules	kWh	2.778×10⁻⁷	3.6 MJ = 1 kWh
Calories	Joules	4.184	100 cal = 418.4 J

Electrical Energy at a Glance

Power (watts) × Time (hours) = Energy (watt-hours)

Device	Power	Time Used	Energy Consumed
LED bulb	10 W	10 hours	100 Wh (0.1 kWh)
Laptop	60 W	8 hours	480 Wh (0.48 kWh)
Refrigerator	150 W	24 hours	3,600 Wh (3.6 kWh)
Air conditioner	3,500 W	8 hours	28,000 Wh (28 kWh)
Electric car charge	7,000 W	10 hours	70,000 Wh (70 kWh)

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Practical Energy Examples

Electricity Consumption & Bills

Typical Household Consumption (USA):

• Small apartment: 500-700 kWh/month
• Average home: 800-1,200 kWh/month
• Large home: 1,500-2,500 kWh/month

Common Appliances (kWh per year):

• Refrigerator: 400-600 kWh/year
• Washing machine: 50-150 kWh/year
• Electric water heater: 4,000-5,000 kWh/year
• Central A/C: 3,000-5,000 kWh/year
• LED lighting (whole house): 200-400 kWh/year

Electricity Cost Calculation:

• US average: $0.12-0.15 per kWh
• Example: 1,000 kWh × $0.13 = $130/month
• 1 kWh = 3,412 BTU = 3.6 MJ

Convert your usage: kWh to Joules →

Food & Nutrition Energy

Daily Caloric Needs:

• Sedentary adult male: 2,000-2,500 kcal/day
• Sedentary adult female: 1,600-2,000 kcal/day
• Active adult: 2,500-3,500 kcal/day
• Athlete (training): 3,000-5,000+ kcal/day

Food Energy Content (per 100g):

• Fat: 900 kcal (37.7 MJ/kg)
• Carbohydrates: 400 kcal (16.7 MJ/kg)
• Protein: 400 kcal (16.7 MJ/kg)
• Alcohol: 700 kcal (29.3 MJ/kg)

Common Foods:

• Banana (medium): 105 kcal (439 kJ)
• Apple (medium): 95 kcal (397 kJ)
• Slice of bread: 80 kcal (335 kJ)
• Chicken breast (100g): 165 kcal (690 kJ)
• Big Mac: 550 kcal (2,300 kJ)

Food Label Confusion:

• "Calorie" (capital C) on US labels = kilocalorie (kcal)
• "calorie" (lowercase c) in science = small calorie (1/1000 of food Calorie)
• kJ on labels (outside US) = kilojoules

Convert food energy: Kilocalories to Joules →

HVAC & Climate Control

Air Conditioner Ratings (cooling capacity):

• Small window unit: 5,000-8,000 BTU/hr (1.5-2.3 kW)
• Medium window unit: 10,000-12,000 BTU/hr (2.9-3.5 kW)
• Large window unit: 14,000-18,000 BTU/hr (4.1-5.3 kW)
• Central A/C (2,000 sq ft home): 36,000-48,000 BTU/hr (10.6-14.1 kW)

Heating Systems:

• Furnace (small home): 40,000-60,000 BTU/hr input
• Furnace (large home): 80,000-120,000 BTU/hr input
• Heat pump: 24,000-60,000 BTU/hr
• Space heater: 5,000-15,000 BTU/hr

Energy Efficiency:

• SEER rating: BTU of cooling per watt-hour of electricity
• Higher SEER = more efficient
• Modern A/C: SEER 14-25
• Old A/C: SEER 8-10

Convert HVAC ratings: BTU to kWh →

Fuel Energy Content

Energy Density (per unit):

• Gasoline: 34.2 MJ/liter (121,300 BTU/gal)
• Diesel: 38.6 MJ/liter (137,400 BTU/gal)
• Natural gas: 37 MJ/m³ (1,000 BTU/ft³)
• Coal: 24-30 MJ/kg
• Wood: 15-20 MJ/kg (dry)

Battery Capacity:

• AAA battery: 1.2 Wh (4,320 J)
• AA battery: 2.5 Wh (9,000 J)
• Smartphone battery: 10-15 Wh
• Laptop battery: 50-100 Wh
• Tesla Model 3 battery: 50-82 kWh
• Home battery (Powerwall): 13.5 kWh

Physics & Mechanical Work

Everyday Energy Examples:

• Lifting 1 kg by 1 meter: 9.8 joules
• Climbing stairs (3m high, 70kg person): 2,058 joules (0.57 Wh)
• Running 1 km: ~300-400 kcal (~1.3-1.7 MJ)
• Bicycle commute (10 km): ~200-300 kcal

Kinetic Energy:

• Car at 60 mph (1,500 kg): 600,000 J (0.167 kWh)
• Baseball pitch (90 mph): 148 J
• Bullet (9mm): 500-600 J

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Common Conversion Mistakes

Mistake 1: Food Calorie vs Scientific Calorie

Error: Thinking 1 food "Calorie" = 1 scientific calorie Correction:

• 1 food Calorie (capital C) = 1 kilocalorie (kcal) = 1,000 scientific calories (small c)
• 1 food Calorie = 4,184 joules, NOT 4.184 joules

Mistake 2: Confusing Power and Energy

Error: Saying "My heater uses 1,500 watts per hour" Correction:

• Power is measured in watts (W)
• Energy is power × time: watt-hours (Wh) or kilowatt-hours (kWh)
• Correct: "My 1,500-watt heater uses 1.5 kWh per hour" or "My heater is rated at 1,500 watts"

Mistake 3: Wrong kWh to Joules Conversion

Error: 1 kWh = 1,000 joules Correction: 1 kWh = 3,600,000 joules = 3.6 megajoules

• Reason: 1 kW = 1,000 watts, 1 hour = 3,600 seconds
• 1,000 W × 3,600 s = 3,600,000 joules

Mistake 4: BTU vs BTU/hr

Error: Using BTU and BTU/hr interchangeably Correction:

• BTU = energy (like kWh)
• BTU/hr = power (like kW)
• Air conditioner rated at "12,000 BTU" actually means 12,000 BTU/hr

Mistake 5: Electricity Cost Confusion

Error: Calculating cost using watts instead of kWh Correction:

• Electric companies charge per kWh, not watts
• Formula: (Watts ÷ 1,000) × Hours × $/kWh = Total cost
• Example: 100W bulb for 10 hours at $0.12/kWh = 0.1 kW × 10 hr × $0.12 = $0.12

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Frequently Asked Questions

How do I convert kWh to joules?

Formula: Joules = kWh × 3,600,000

Examples:

• 1 kWh = 3,600,000 J = 3.6 MJ
• 10 kWh = 36,000,000 J = 36 MJ
• 100 kWh = 360,000,000 J = 360 MJ

Why 3,600,000?

• 1 kilowatt = 1,000 watts
• 1 hour = 3,600 seconds
• 1 kWh = 1,000 W × 3,600 s = 3,600,000 joules

Convert kWh to Joules →

How many calories are in a food Calorie?

1 food "Calorie" (capital C) = 1,000 small calories (lowercase c)

Important distinction:

• Food labels (USA): "Calorie" = kilocalorie (kcal)
• Food labels (international): Often show both kcal and kJ
• Scientific: "calorie" (small c) = 4.184 joules

Conversions:

• 1 food Calorie = 1 kcal = 1,000 cal = 4,184 J = 4.184 kJ
• 100 food Calories = 100 kcal = 418,400 J = 418.4 kJ

Why the confusion? Food labels use "Calorie" (capital C) as shorthand for kilocalorie, but this isn't universally understood.

Convert Kilocalories to Joules →

What is a kilowatt-hour (kWh)?

A kilowatt-hour is the amount of energy used by a 1-kilowatt device running for 1 hour.

Examples:

• 1,000-watt microwave for 1 hour = 1 kWh
• 100-watt light bulb for 10 hours = 1 kWh
• 2,000-watt space heater for 30 minutes = 1 kWh

Why kWh instead of kW?

• kW (kilowatt) = power (rate of energy use)
• kWh (kilowatt-hour) = energy (total amount consumed)
• Electric companies charge for energy (kWh), not power (kW)

Typical costs:

• USA average: $0.12-0.15 per kWh
• Europe: €0.20-0.30 per kWh
• California: $0.25-0.35 per kWh (tiered)

How do I calculate electricity costs?

Formula: Cost = (Watts ÷ 1,000) × Hours × Price per kWh

Step-by-step example (1,500W heater, 8 hours/day, $0.13/kWh):

1. Convert to kilowatts: 1,500 W ÷ 1,000 = 1.5 kW
2. Calculate energy: 1.5 kW × 8 hr = 12 kWh
3. Calculate cost: 12 kWh × $0.13 = $1.56 per day
4. Monthly cost: $1.56 × 30 days = $46.80

Quick formula for daily cost:

• Daily cost = (Watts × Hours ÷ 1,000) × $/kWh

How do I convert BTU to kWh?

Formula: kWh = BTU × 0.000293071

Examples:

• 10,000 BTU = 2.93 kWh
• 12,000 BTU (1-ton A/C) = 3.52 kWh
• 24,000 BTU (2-ton A/C) = 7.03 kWh
• 100,000 BTU (furnace) = 29.3 kWh

Quick approximation: Divide BTU by 3,412

• 10,000 BTU ÷ 3,412 ≈ 2.93 kWh

Why this matters:

• Air conditioners rated in BTU/hr
• Electricity billed in kWh
• Conversion helps calculate operating costs

Convert BTU to kWh →

What's the difference between Wh and kWh?

Wh (watt-hour) vs kWh (kilowatt-hour):

• 1 kWh = 1,000 Wh
• Wh for small devices (batteries, phone chargers)
• kWh for large devices and utility billing

Examples:

• Phone battery: 15 Wh (0.015 kWh)
• Laptop battery: 80 Wh (0.08 kWh)
• Electric car battery: 60,000 Wh (60 kWh)
• Monthly home use: 900,000 Wh (900 kWh)

Usage:

• Battery capacity: Wh or mAh
• Utility bills: kWh
• Solar panels: kWh/day or kWh/year

How many joules in a food Calorie?

1 food Calorie = 4,184 joules = 4.184 kilojoules

Important: Food "Calorie" (capital C) = kilocalorie (kcal)

Examples:

• 100-Calorie snack = 418,400 joules = 418.4 kJ
• 500-Calorie meal = 2,092,000 joules = 2,092 kJ
• 2,000-Calorie diet = 8,368,000 joules = 8.368 MJ

International food labels:

• Show both kcal AND kJ
• Example: "250 kcal (1,046 kJ)"

Convert Kilocalories to Joules →

How much does it cost to run an appliance?

Daily Cost Formula: Cost/day = (Watts ÷ 1,000) × Hours/day × $/kWh

Examples at $0.13/kWh:

Always-on devices:

• Refrigerator (150W, 24hr): $0.47/day = $14/month
• WiFi router (10W, 24hr): $0.03/day = $1/month
• Desktop PC (200W, 8hr): $0.21/day = $6/month

Seasonal devices:

• Window A/C (1,000W, 8hr): $1.04/day = $31/month
• Space heater (1,500W, 6hr): $1.17/day = $35/month
• Pool pump (1,100W, 8hr): $1.14/day = $34/month

Occasional use:

• Clothes dryer (3,000W, 1hr): $0.39 per load
• Dishwasher (1,800W, 2hr): $0.47 per load
• Electric oven (2,400W, 1hr): $0.31 per use

Quick Reference Card

Essential Conversions:

• 1 kWh = 3,600,000 J = 3.6 MJ
• 1 kWh = 3,412 BTU
• 1 BTU = 1,055 J
• 1 food Calorie (kcal) = 4,184 J = 4.184 kJ
• 1 kWh = 860 kcal

Energy Costs (USA average $0.13/kWh):

• 1 kWh = $0.13
• 100W for 10 hours = 1 kWh = $0.13
• 1,000W for 1 hour = 1 kWh = $0.13

Common Energy Amounts:

• Climbing 3m stairs (70kg): 2,058 J
• Banana: 439 kJ (105 kcal)
• Daily food (2,000 kcal): 8.4 MJ
• Gallon of gas: 121 MJ (34 kWh)
• Tesla battery: 75 kWh (270 MJ)

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Related Converters

Power & Electrical:

• Power Converter → - Watts, horsepower, BTU/hr

Physical Measurements:

• Force Converter → - Newtons, pounds-force
• Pressure Converter → - PSI, bar, atmospheres

Browse All:

• All Converters → - Complete list
• Conversion Guides → - Measurement tutorials

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Popular Energy Conversion Pairs

Electricity:

• kWh to Joules →
• Joules to kWh →
• Watt-hour to Joules →
• Megajoules to kWh →

Food & Nutrition:

• Kilocalories to Joules →
• Calories to Joules →
• Kilocalories to kWh →

HVAC & Heating:

• BTU to kWh →
• BTU to Joules →
• Therm to kWh →
• kWh to BTU →

Scientific:

• Joules to Kilojoules →
• Megajoules to Joules →

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