Bar (bar) - Unit Information & Conversion
🔄 Quick Convert Bar
What is a Bar?
The bar (symbol: bar) is a metric unit of pressure defined as exactly 100,000 pascals (Pa) or 100 kilopascals (kPa). Introduced in 1909, the bar was deliberately chosen to approximate standard atmospheric pressure at sea level (1.01325 bar = 1 atmosphere), making it intuitively meaningful for practical applications. The bar has become the predominant pressure unit in European automotive specifications (tire pressures typically 2.0-2.5 bar), industrial hydraulic and pneumatic systems worldwide, scuba diving (tank pressures 200-300 bar), and meteorology (as millibars: 1 mbar = 0.001 bar). While not an official SI unit, the bar is widely accepted for use alongside SI units due to its exact decimal relationship to the pascal (1 bar = 10⁵ Pa) and its widespread adoption in engineering, manufacturing, and daily life. The bar provides a practical middle ground between the very small pascal and the non-metric PSI, with 1 bar equaling approximately 14.5 PSI or 0.987 atmospheres.
History of the Bar
The bar was introduced in 1909 by British meteorologist William Napier Shaw (1854-1945), who proposed it as a rational metric alternative to the chaotic mix of pressure units then in use—atmospheres, mmHg, PSI, and various local standards. Shaw derived the name "bar" from the Greek word "baros" (βάρος) meaning weight, the same root as "barometer." He deliberately defined 1 bar = 10⁶ dynes/cm² (in CGS units) = 10⁵ Pa (in SI units), which conveniently approximated one atmosphere (1 atm = 1.01325 bar), making the bar immediately intuitive for meteorology and engineering. The bar gained rapid adoption in European meteorology, where the millibar (mbar = 0.001 bar = 100 Pa) became the standard for reporting atmospheric pressure throughout the 20th century. The International Committee for Weights and Measures (CIPM) officially recognized the bar in 1982 as acceptable for use with SI units, acknowledging its widespread industrial and commercial adoption. Today, the bar dominates tire pressure specifications in Europe and Asia (replacing PSI), hydraulic system ratings worldwide, scuba diving standards, and remains the preferred unit in many engineering disciplines for its convenient scale and exact relationship to SI units.
Quick Answer
What is a bar? The bar is a metric unit of pressure equal to 100,000 pascals (Pa) or 100 kilopascals (kPa). It approximates atmospheric pressure at sea level (1.01325 bar = 1 atmosphere), making it intuitive for practical use. The bar is the standard pressure unit throughout Europe for tire inflation (typical car tire: 2.2 bar = 32 PSI), industrial hydraulic systems, scuba diving tank pressures (200-300 bar), and meteorology (as millibars). 1 bar = 100 kPa = 100,000 Pa = 14.5 PSI = 0.987 atm. Use our pressure converter for all your bar conversions.
Quick Comparison Table
| Pressure Unit | Equivalent to 1 Bar | Common Uses |
|---|---|---|
| Bar | 1 bar | European tires, industrial hydraulics, scuba diving |
| Pascal (Pa) | 100,000 Pa | SI fundamental unit, scientific research |
| Kilopascal (kPa) | 100 kPa | Engineering specifications, international tire standards |
| Megapascal (MPa) | 0.1 MPa | Material strength, ultra-high pressure (100 bar = 10 MPa) |
| PSI | 14.5038 PSI | US/UK tire pressure, American industrial equipment |
| Atmosphere (atm) | 0.986923 atm | Diving depths, gas storage, historical reference |
| mmHg/Torr | 750.062 mmHg | Blood pressure, vacuum systems, medical |
| Millibar (mbar) | 1,000 mbar | Meteorology (identical to hectopascal: 1 mbar = 1 hPa) |
Real-world anchors: Standard atmospheric pressure = 1.01325 bar = 101.325 kPa = 101,325 Pa = 1,013.25 mbar = 14.7 PSI = 1 atm
Definition and Standards
The bar is defined as:
Fundamental Definition
1 bar = 100,000 Pa (exactly) 1 bar = 100 kPa (exactly) 1 bar = 0.1 MPa (exactly)
In CGS units (historical): 1 bar = 10⁶ dynes/cm²
Why 100,000 Pascals?
The bar was deliberately chosen to create a practical, metric-friendly pressure unit that:
- Approximates atmospheric pressure: 1 bar ≈ 1 atm (actual: 1.01325 bar = 1 atm)
- Uses round numbers: 100,000 Pa = 100 kPa (easy mental math)
- Bridges small and large pressures: Larger than Pa, smaller than MPa
- Decimal relationship to SI: Exact powers of 10 conversion to Pa/kPa/MPa
Standard Conversions
- 1 bar = 100,000 Pa (exactly)
- 1 bar = 100 kPa (exactly)
- 1 bar = 0.1 MPa (exactly)
- 1 bar = 14.5038 PSI
- 1 bar = 0.986923 atm
- 1 bar = 1,000 mbar (millibars)
- 1 bar = 10 dbar (decibars—oceanography)
- 1 bar = 750.062 mmHg (Torr)
- 1 bar = 29.53 inches Hg
Relationship to Standard Atmosphere
- 1 atmosphere (atm) = 1.01325 bar (exactly)
- 1 bar = 0.986923 atm
- Difference: ~1.3%, small enough for many practical purposes to treat as equal
Millibar (mbar) — Meteorology Standard
1 millibar (mbar) = 0.001 bar = 100 Pa = 1 hectopascal (hPa)
Weather reports worldwide use millibars/hectopascals:
- Standard sea-level pressure: 1,013.25 mbar = 1.01325 bar
- Weather range: 980-1,050 mbar (0.98-1.05 bar)
- Hurricane pressure: <920 mbar (<0.92 bar)
Note: Meteorologists now officially use hectopascals (hPa) instead of millibars, but they're numerically identical: 1 mbar = 1 hPa.
History and Evolution
William Napier Shaw and the Bar's Creation (1909)
Sir William Napier Shaw (1854-1945) was a pioneering British meteorologist who revolutionized weather forecasting and atmospheric science. As Director of the British Meteorological Office (1905-1920), Shaw faced a practical problem: meteorologists, engineers, and scientists used wildly inconsistent pressure units, making international data sharing difficult.
The Problem (Pre-1909):
- Meteorology: Inches of mercury (inHg) in UK/US, millimeters of mercury (mmHg) in Europe
- Engineering: Pounds per square inch (PSI) in English-speaking countries
- Science: Atmospheres (atm), technical atmospheres (at = 1 kgf/cm²), various CGS units
- Result: Confusion, conversion errors, lack of standardization
Shaw's Solution: Create a metric pressure unit that:
- Approximates atmospheric pressure for intuitive meaning (1 bar ≈ 1 atm)
- Uses metric/decimal system for easy calculation
- Fits CGS and later SI frameworks with exact relationships
- Provides practical scale between very small Pa and large atm
Etymology: Shaw chose "bar" from Greek baros (βάρος = weight), the same root as:
- Barometer (baros + metron = weight measurer)
- Barograph (baros + graphein = weight recorder)
- Isobar (isos + baros = equal weight/pressure)
Definition (1909): 1 bar = 10⁶ dynes/cm² (CGS units)
When SI units were adopted in 1960, this translated to: 1 bar = 10⁵ Pa = 100,000 Pa = 100 kPa
Millibar and Meteorology (1910s-1990s)
Rapid adoption: The millibar (mbar = 0.001 bar) became the dominant meteorological pressure unit by the 1920s-1930s, appearing on:
- Weather maps (isobars labeled in mbar)
- Barometer scales (replacing inches/mm Hg)
- Aviation altimeter settings
- Synoptic weather charts worldwide
Why millibar succeeded:
- Sea-level pressure = 1,013 mbar (easy three-digit number)
- Weather variations 980-1,050 mbar fit human-scale numbers
- Metric decimal system simplified calculations
- International meteorological cooperation adopted it as standard
Transition to Hectopascal (1990s): When SI units were fully standardized, meteorologists transitioned from "millibar" to "hectopascal" (hPa) terminology:
- 1 mbar = 1 hPa (numerically identical)
- Weather reports changed wording but not numbers: "1015 mbar" → "1015 hPa"
- Many regions still colloquially use "millibar" despite official hPa standard
Industrial and Automotive Adoption (1950s-Present)
European Industrial Standardization (1950s-1970s):
- Hydraulic systems: Bar replaced PSI in European manufacturing
- Pneumatic tools: Compressed air specifications in bar (6-10 bar standard)
- Pressure vessel codes: European standards (DIN, EN) used bar
- Scuba diving: Bar became universal for tank pressure ratings (200-300 bar)
Automotive Tire Pressure (1960s-2000s):
- European transition: Car manufacturers adopted bar for tire specifications
- Practical numbers: Passenger car tires 2.0-2.5 bar (vs 29-36 PSI)
- Sidewall labeling: Dual marking "32 PSI / 2.2 bar" became global standard
- Current status: Europe, Asia, Middle East, Africa primarily use bar; US/UK still predominantly PSI
Global Engineering (1980s-Present):
- ISO standards: Many use bar alongside MPa for hydraulic/pneumatic specifications
- Material datasheets: Bar appears in pressure-temperature ratings
- Commercial equipment: European/Asian machinery rated in bar
CIPM Recognition (1982)
The International Committee for Weights and Measures (CIPM) officially recognized the bar in 1982 as acceptable for use with the International System of Units (SI), despite not being an SI unit itself.
Reasoning:
- Widespread industrial and commercial use made elimination impractical
- Exact decimal relationship to SI (1 bar = 10⁵ Pa) ensured compatibility
- No confusion with SI units due to distinct name and symbol
- Valuable for expressing pressures in human-scale numbers (tire: 2.2 bar vs 220,000 Pa)
Status Today:
- Not SI, but SI-compatible: Bar allowed in contexts where practical
- Scientific literature: Pascals preferred, bar acceptable for applied engineering
- Industry standard: Bar dominates hydraulics, automotive, diving worldwide
- Coexistence: Bar and PSI used alongside each other in international trade
Real-World Examples and Applications
Atmospheric and Weather Pressure
Standard Atmospheric Pressure (Sea Level):
- 1.01325 bar = 1,013.25 mbar = 101.325 kPa = 1 atm
- Weather reports: "Pressure is 1015 mbar" = 1.015 bar
- Rounded approximation: 1 bar ≈ 1 atmosphere
Weather Variations:
- High pressure system: 1.020-1.060 bar (1,020-1,060 mbar) = clear, stable weather
- Normal range: 1.000-1.020 bar
- Low pressure system: 0.980-1.000 bar (980-1,000 mbar) = storms, precipitation
- Tropical storm: 0.950-0.980 bar (950-980 mbar)
- Hurricane (Category 1-2): 0.920-0.950 bar (920-950 mbar)
- Hurricane (Category 4-5): <0.920 bar (<920 mbar)—catastrophic
- Record low: 0.870 bar (Typhoon Tip, 1979)
- Record high: 1.084 bar (Siberia, 1968)
Altitude Effects:
- Sea level: 1.013 bar (14.7 PSI)
- 1,000 m (3,281 ft): 0.900 bar (13.1 PSI)
- 1,600 m (Denver, 5,280 ft): 0.830 bar (12.0 PSI)
- 2,500 m (8,202 ft): 0.746 bar (10.8 PSI)
- 5,000 m (16,404 ft): 0.540 bar (7.8 PSI)—Everest Base Camp
- 8,849 m (29,032 ft): 0.337 bar (4.9 PSI)—Mount Everest summit
- 10,000 m (32,808 ft): 0.265 bar (3.8 PSI)—commercial jet cruise altitude (outside)
- Airplane cabin (pressurized): 0.750-0.800 bar equivalent (7,500-8,000 ft elevation)
Automotive Tire Pressure (European Standard)
Passenger Car Tires:
- Compact car (Honda Civic, VW Golf): 2.0-2.2 bar (29-32 PSI)
- Mid-size sedan (Toyota Camry, Ford Mondeo): 2.2-2.4 bar (32-35 PSI)
- SUV/Crossover (Honda CR-V, VW Tiguan): 2.3-2.5 bar (33-36 PSI)
- Sports car (Porsche 911): 2.5-3.0 bar (36-44 PSI)—higher for performance
- Electric vehicle (Tesla Model 3): 2.9 bar (42 PSI)—higher due to weight
- Light truck/Van: 2.4-2.8 bar (35-40 PSI)
Motorcycle and Bicycle Tires:
- Motorcycle (street): 2.0-2.9 bar (29-42 PSI)—varies front/rear
- Scooter: 1.8-2.5 bar (26-36 PSI)
- Bicycle (mountain bike): 1.7-3.1 bar (25-45 PSI)—lower for traction
- Bicycle (hybrid/city): 3.5-5.5 bar (50-80 PSI)
- Bicycle (road racing): 6.0-8.5 bar (87-123 PSI)—high for low rolling resistance
Commercial Vehicle Tires:
- Delivery van: 3.5-4.5 bar (51-65 PSI)
- Heavy truck (tractor-trailer): 5.5-9.0 bar (80-130 PSI)
- Bus: 7.0-9.0 bar (102-130 PSI)
- Aircraft tire: 10-15 bar (145-218 PSI)—extreme pressure for weight
Temperature Effects:
- Tire pressure increases ~0.1 bar (1.5 PSI) per 10°C (18°F) temperature rise
- Cold morning: 2.2 bar → After highway driving (hot tires): 2.4-2.5 bar
- Always check tire pressure when tires are cold (before driving)
Industrial Hydraulic and Pneumatic Systems
Compressed Air (Pneumatic Systems):
- Shop air compressor: 6-10 bar (87-145 PSI)—standard industrial
- Pneumatic tools (impact wrench, air drill): 6.2 bar (90 PSI) typical operating
- Pneumatic conveying: 4-7 bar (58-102 PSI)
- Spray painting: 2-4 bar (29-58 PSI)
- Brake systems (trucks/trains): 8-10 bar (116-145 PSI)
- Factory automation: 6 bar (87 PSI) standard
Hydraulic Systems:
- Hydraulic car jack: 10-20 bar (145-290 PSI)
- Power steering: 70-140 bar (1,015-2,030 PSI)
- Forklift hydraulics: 150-200 bar (2,175-2,900 PSI)
- Excavator/backhoe: 200-350 bar (2,900-5,075 PSI)
- Industrial hydraulic press: 700-1,000 bar (10,150-14,500 PSI)
- Injection molding machine: 1,500-2,000 bar (21,750-29,000 PSI)
- Waterjet cutter: 3,000-4,000 bar (43,500-58,000 PSI)—cuts steel
Water and Fluid Systems:
- Municipal water supply: 3-8 bar (43-116 PSI)—typical home delivery
- Garden hose: 2-4 bar (29-58 PSI)
- Pressure washer (consumer): 100-150 bar (1,450-2,175 PSI)
- Pressure washer (industrial): 150-250 bar (2,175-3,625 PSI)
- Fire hydrant: 5-10 bar (72-145 PSI)
- Espresso machine: 9 bar (130 PSI)—optimal extraction pressure
- Steam boiler (low pressure): 10-15 bar (145-218 PSI)
- High-pressure boiler: 100-200 bar (1,450-2,900 PSI)
Scuba Diving and Gas Cylinders
Scuba Diving Tank Pressures:
- Aluminum 80 cu ft tank (full): 207 bar (3,000 PSI)—US standard
- Steel tank (full): 232 bar (3,365 PSI)
- Aluminum 80 tank (full, Europe): 200 bar (2,900 PSI)
- Steel 12L tank (full, Europe): 232-300 bar (3,365-4,350 PSI)
- Reserve pressure: 50 bar (725 PSI)—minimum to surface safely
- Working pressure: Tank rated for 200-300 bar continuous use
- Hydrostatic test pressure: 1.5× working pressure (300-450 bar for testing)
Depth Pressure (absolute pressure underwater):
- Surface: 1 bar (14.7 PSI) = 1 atmosphere absolute
- 10 m depth (33 ft): 2 bar = tank regulator delivers air at 2 bar
- 20 m depth (66 ft): 3 bar
- 30 m depth (98 ft): 4 bar—recreational diving limit
- 40 m depth (130 ft): 5 bar—advanced open water limit
- 50 m depth (164 ft): 6 bar
- 100 m depth (328 ft): 11 bar—technical/commercial diving
Gas Cylinders (Industrial):
- Propane tank (BBQ): 15-20 bar (218-290 PSI)
- Oxygen cylinder (medical/welding): 150-200 bar (2,175-2,900 PSI)
- Nitrogen/argon cylinder: 200 bar (2,900 PSI)
- Helium cylinder: 200-300 bar (2,900-4,350 PSI)
- Hydrogen fuel (vehicle, 700 bar standard): 700 bar (10,150 PSI)—carbon fiber composite tanks
- CNG (compressed natural gas): 200-250 bar (2,900-3,625 PSI)
Engine and Automotive Systems
Engine Oil Pressure:
- Idle pressure: 7-14 bar (102-203 PSI)—minimum to prevent damage
- Highway/cruise: 28-41 bar (406-595 PSI)
- Cold start (thick oil): 35-55 bar (507-798 PSI)
Fuel Systems:
- Carburetor fuel pump: 0.2-0.4 bar (3-6 PSI)
- Port fuel injection: 3-5 bar (43-72 PSI)
- Gasoline direct injection (GDI): 50-200 bar (725-2,900 PSI)
- Common rail diesel: 1,600-2,500 bar (23,200-36,250 PSI)—ultra-high pressure
Turbocharger/Supercharger Boost:
- Mild turbo (economy): 0.5-1.0 bar boost (7-15 PSI boost) = 1.5-2.0 bar absolute
- Performance turbo: 1.0-1.5 bar boost (15-22 PSI boost) = 2.0-2.5 bar absolute
- High-performance/racing: 2.0-3.0 bar boost (29-44 PSI boost) = 3.0-4.0 bar absolute
Air Conditioning:
- Low-side pressure: 2-3 bar (29-44 PSI)
- High-side pressure: 15-25 bar (218-363 PSI)—depends on refrigerant, temperature
Materials and Engineering
Pressure Vessel Design (working pressures in bar):
- Low-pressure vessels: <5 bar (72 PSI)—storage tanks
- Medium-pressure vessels: 5-50 bar (72-725 PSI)—process equipment
- High-pressure vessels: 50-500 bar (725-7,250 PSI)—reactors, autoclaves
- Ultra-high-pressure: >500 bar (>7,250 PSI)—specialized industrial processes
Pipeline Pressures:
- Natural gas distribution (local): 5-25 bar (72-363 PSI)
- Natural gas transmission (long-distance): 50-100 bar (725-1,450 PSI)
- Hydrogen pipeline: 10-100 bar (145-1,450 PSI)
- CO₂ pipeline (carbon capture): 150-200 bar (2,175-2,900 PSI)
Laboratory and Scientific Equipment:
- Autoclave (sterilization): 2-3 bar (29-44 PSI), 121-134°C
- Pressure reactor: 10-300 bar (145-4,350 PSI) depending on chemistry
- Supercritical fluid extraction: 100-500 bar (1,450-7,250 PSI)
- Diamond anvil cell: Up to 5,000,000 bar (5,000 GPa)—extreme conditions research
Common Uses Across Industries
Automotive and Transportation
- Tire pressure specifications: Universal in Europe, Asia, Africa (2-2.5 bar typical cars)
- Vehicle manuals: All European/Asian manufacturers specify bar
- Tire pressure monitoring systems (TPMS): Display in bar or PSI based on region
- Service station air pumps: Labeled in bar throughout Europe/Asia
Industrial Manufacturing
- Hydraulic machinery: European/Asian equipment rated in bar (excavators, presses)
- Pneumatic systems: Compressed air specifications worldwide (6-10 bar standard)
- Process equipment: Pressure ratings in bar (reactors, heat exchangers, distillation)
- Quality control: Pressure testing specifications in bar
Scuba Diving and Water Sports
- Universal diving standard: Tank pressures worldwide rated in bar (200-300 bar)
- Dive computers: Display depth pressure in bar
- Dive tables: Pressure calculations in bar
- Compressor stations: Fill pressures specified in bar
Meteorology and Aviation
- Weather reports: Atmospheric pressure in millibars (mbar) or hectopascals (hPa)
- Weather maps: Isobars (lines of equal pressure) labeled in mbar
- Altimeter settings: Some regions use hectopascals (1 hPa = 1 mbar = 0.001 bar)
- Barometers: Scales often include bar/mbar markings
Medical and Healthcare
- Hyperbaric oxygen therapy: Chamber pressures 2-3 bar absolute (2-3 ATA)
- Respiratory equipment: Some ventilators display pressure in mbar
- Autoclaves: Sterilization at 2.0-2.2 bar, 121-134°C
- Medical gas cylinders: Oxygen/air tanks rated in bar
Energy and Utilities
- Natural gas distribution: Pipeline pressures in bar (5-100 bar)
- Steam systems: Boiler and turbine pressures in bar
- Hydrogen infrastructure: Fuel cell vehicle tanks 350-700 bar
- Compressed air energy storage: 40-80 bar in underground caverns
Conversion Guide
Bar to Other Units
Bar to Pascal (Pa):
- Formula: Pa = bar × 100,000
- Example: 2.5 bar = 250,000 Pa
- Use: Scientific calculations, SI compliance
Bar to Kilopascal (kPa):
- Formula: kPa = bar × 100 (exactly)
- Example: 2.2 bar = 220 kPa
- Use: Engineering specifications, international standards
- Easiest conversion: Just multiply by 100!
Bar to Megapascal (MPa):
- Formula: MPa = bar ÷ 10 (or bar × 0.1)
- Example: 350 bar = 35 MPa
- Use: High-pressure hydraulics, material strength
Bar to PSI:
- Formula: PSI = bar × 14.5038
- Example: 2.2 bar = 31.9 PSI
- Use: US/UK specifications, American equipment
- Approximation: Multiply by ~14.5 or 15
Bar to Atmosphere (atm):
- Formula: atm = bar × 0.986923 (or bar ÷ 1.01325)
- Example: 3.0 bar = 2.96 atm
- Use: Diving calculations, gas storage
- Approximation: 1 bar ≈ 1 atm (1.3% difference)
Bar to mmHg (Torr):
- Formula: mmHg = bar × 750.062
- Example: 1.0 bar = 750 mmHg
- Use: Vacuum systems, medical applications
Bar to Millibar (mbar):
- Formula: mbar = bar × 1,000 (exactly)
- Example: 1.013 bar = 1,013 mbar
- Use: Meteorology, atmospheric pressure
- Note: 1 mbar = 1 hPa (hectopascal)
Quick Mental Math Approximations
Bar to PSI (~14.5× or ~15× rule):
- Multiply bar by 14.5 for accurate PSI
- Multiply bar by 15 for rough PSI
- Examples:
- 2 bar × 14.5 = 29 PSI (exact: 29.0 PSI)
- 2.2 bar × 14.5 = 31.9 PSI (exact: 31.9 PSI)
- 10 bar × 15 ≈ 150 PSI (exact: 145 PSI)
PSI to Bar (~÷15 or ×0.07 rule):
- Divide PSI by 15 for rough bar
- Multiply PSI by 0.069 for accurate bar
- Examples:
- 30 PSI ÷ 15 = 2.0 bar (exact: 2.07 bar)
- 32 PSI ÷ 15 ≈ 2.1 bar (exact: 2.20 bar)
- 100 PSI ÷ 15 ≈ 6.7 bar (exact: 6.89 bar)
Bar to kPa (×100, exact):
- Just multiply by 100 (add two zeros)
- Examples:
- 1 bar = 100 kPa
- 2.5 bar = 250 kPa
- 200 bar = 20,000 kPa = 20 MPa
Bar to atm (approximately equal):
- For rough calculations: 1 bar ≈ 1 atm
- For accuracy: 1 bar = 0.987 atm, or 1 atm = 1.013 bar
- Difference only matters for precision work
Atmospheric pressure conversions (memorize):
- 1 atm = 1.01325 bar ≈ 1 bar (rough)
- 1 atm = 101.325 kPa = 101,325 Pa
- 1 atm = 14.7 PSI
- 1 atm = 1,013.25 mbar = 1,013.25 hPa
- 1 atm = 760 mmHg
Conversion Table Reference
| From | To PSI | To kPa | To MPa | To atm | To mmHg | To mbar |
|---|---|---|---|---|---|---|
| 1 bar | 14.504 | 100 | 0.1 | 0.9869 | 750.06 | 1,000 |
| 2 bar | 29.008 | 200 | 0.2 | 1.974 | 1,500 | 2,000 |
| 5 bar | 72.519 | 500 | 0.5 | 4.934 | 3,750 | 5,000 |
| 10 bar | 145.04 | 1,000 | 1.0 | 9.869 | 7,501 | 10,000 |
| 100 bar | 1,450.4 | 10,000 | 10 | 98.69 | 75,006 | 100,000 |
| 200 bar | 2,900.8 | 20,000 | 20 | 197.38 | 150,012 | 200,000 |
Common Conversion Mistakes
Mistake 1: Confusing Bar with PSI by Factor of 14.5
Wrong: "Tire pressure 30 bar" (would be 435 PSI—truck tire, not car!) Right: "Tire pressure 2.0-2.2 bar" (29-32 PSI—typical car tire)
Why it matters: Bar and PSI are completely different scales. Always check which unit your gauge reads. European gauges show bar, American gauges show PSI.
Mistake 2: Treating Bar and Atmosphere as Identical
Wrong: Using 1 bar = 1 atm for precise calculations Right: 1 atm = 1.01325 bar (1.3% difference)
Why it matters:
- Rough work: 1 bar ≈ 1 atm is acceptable (weather, casual discussion)
- Precision work: Use exact conversion (diving decompression, gas laws, scientific calculations)
- Scuba diving: 10 meters depth = 2 bar, not 2 atm (though divers often say "2 atmospheres" colloquially)
Mistake 3: Forgetting Gauge vs Absolute Pressure
Wrong: "Tire gauge reads 2.2 bar, so absolute pressure is 2.2 bar" Right: "Tire gauge reads 2.2 bar gauge = 2.2 + 1.013 = 3.2 bar absolute"
Why it matters:
- Gauge pressure (bar g): Pressure above atmospheric (tire gauges, hydraulic gauges)
- Absolute pressure (bar a): Total pressure including atmospheric (thermodynamics, gas laws)
- Most gauges read gauge pressure; thermodynamic calculations need absolute pressure
Mistake 4: Mixing Millibar and Bar
Wrong: "Weather pressure is 1013 bar" (would be 1,000× atmospheric—impossible!) Right: "Weather pressure is 1013 mbar" = 1.013 bar
Why it matters:
- Millibar (mbar) = 0.001 bar = meteorology standard
- Bar = 1,000 mbar = engineering/industrial standard
- Three orders of magnitude difference—critical to avoid confusion
Mistake 5: Using Wrong PSI Conversion Factor
Wrong: bar × 10 = PSI (gives 20 PSI for 2 bar—way off) Right: bar × 14.5038 = PSI (gives 29.0 PSI for 2 bar—correct)
Why it matters: ~4.5 PSI error per bar accumulates. For tire pressure, could lead to under-inflation (poor handling, tire wear) or over-inflation (harsh ride, blowout risk).
Mistake 6: Assuming Bar is an SI Unit
Wrong: "Bar is the SI unit of pressure" Right: "Pascal (Pa) is the SI unit; bar is metric-compatible but not official SI"
Why it matters:
- Scientific papers: Should use Pa/kPa/MPa (SI units)
- Engineering/industry: Bar is widely accepted and practical
- International standards: Some require SI (Pa), others accept bar
- Know your audience: academia vs industry vs commercial
Bar Conversion Formulas
To Pascal:
To Kilopascal:
To Megapascal:
To Hectopascal:
To Millibar:
To Atmosphere:
To Technical Atmosphere:
To Torr:
To Millimeter of Mercury:
To Inch of Mercury:
To Pound per Square Inch:
To Kilopound per Square Inch:
To Kilogram-force per Square Centimeter:
To Kilogram-force per Square Meter:
To Millimeter of Water Column:
To Inch of Water Column:
Frequently Asked Questions
One bar = 100,000 pascals (Pa) = 100 kilopascals (kPa). Physical interpretation:
- One bar approximately equals atmospheric pressure at sea level (actual: 1.013 bar)
- One bar = pressure from a 10-meter (33-foot) column of water
- One bar = 10 newtons of force distributed over 1 cm² (10 N/cm²) Why it's practical: The bar bridges the gap between the very small pascal (101,325 Pa for atmospheric pressure) and the non-metric atmosphere/PSI. Tire pressure of 2.2 bar is easier to remember and communicate than 220,000 Pa or 220 kPa.
Convert Bar
Need to convert Bar to other pressure units? Use our conversion tool.