What is pressure?

Pressure is force per unit area – how concentrated a force is over a surface. The SI unit is the pascal (Pa = 1 N/m²) but real-world contexts use many other units: bar (close to atmospheric pressure), psi (pounds per square inch, used in tire pressure US/UK), atmospheres (atm, scientific reference), millimeters of mercury (mmHg, blood pressure), inches of mercury (inHg, weather barometers), torr (vacuum technology), and inches of water (inH2O, HVAC ducts). Understanding pressure is essential for: tire inflation (under-inflated tires cause fuel inefficiency and blowouts), blood pressure monitoring (120/80 mmHg normal), scuba diving (1 atm per 10m depth), cooking (pressure cookers operate at 1.5-2 atm above ambient), and weather (low/high pressure systems).

How to use this tool

1. Enter pressure value — The amount you want to convert.
2. Select ‘from’ unit — 9+ options: Pa, kPa, bar, mbar, atm, psi, torr (mmHg), inHg, inH2O.
3. Read conversions — All other units show equivalents. Easy to translate ‘120/80 mmHg’ (blood pressure) to other scales.

Pressure unit conversions

All conversions via pascal (SI base):

• 1 Pa = 1 N/m² (tiny unit)
• 1 kPa = 1,000 Pa
• 1 bar = 100,000 Pa = 100 kPa (close to atmospheric pressure)
• 1 mbar = 100 Pa
• 1 atm (standard atmosphere) = 101,325 Pa = 1.01325 bar
• 1 psi = 6,894.76 Pa = 6.895 kPa
• 1 torr / mmHg = 133.322 Pa
• 1 inHg = 3,386.39 Pa
• 1 inH2O = 248.84 Pa

Quick references:

• Sea level atmosphere: 1 atm = 101.325 kPa = 14.7 psi = 1013 mbar
• Tire pressure (recommended 30-35 psi): ~207-241 kPa
• Blood pressure 120/80 mmHg: 16/10.7 kPa
• Scuba: every 10m depth adds 1 atm = 14.7 psi

Examples

• Tire pressure 32 psi: 221 kPa, 2.21 bar, 1.66 atm, 1,656 mmHg
• Blood pressure 120 mmHg systolic: 16 kPa, 0.158 atm, 2.32 psi
• Pressure cooker (1.5 atm above ambient): 152 kPa above ambient, total ~250 kPa = 36 psi gauge
• Mariana Trench (~11 km deep, ~1086 atm): 109.5 MPa, 15,750 psi – crushing!
• Standard atmosphere (sea level): 101,325 Pa = 1013 mbar = 14.7 psi
• Mount Everest summit (~33 kPa): 0.326 atm, 4.78 psi – 1/3 sea level
• Soda can interior (~3 atm): 304 kPa, 44 psi (don’t shake!)
• F1 tire (28 psi cold, 32 psi hot): Pressure changes 1 psi per 10°F temperature change

Tips & best practices

• Tire pressure: check when tires are COLD (driving heats them up). Recommended PSI is on the door jamb sticker, not the tire sidewall
• Higher altitudes: lower atmospheric pressure means slightly less efficient combustion engines (3% loss per 1000m altitude). Cars compensate with turbocharger
• Scuba diving: pressure doubles at 10m, triples at 20m. Decompression is critical – rising too fast can cause ‘bends’
• Cooking at altitude: lower pressure means water boils below 100°C. Add 1 min cooking time per 300m altitude
• Weather: high pressure (above 1020 mbar) = clear sunny days. Low pressure (below 1000 mbar) = clouds, rain, storms
• Hypertension diagnosis: systolic >140 mmHg or diastolic >90 mmHg sustained. Healthy: 120/80 mmHg. Monitor regularly after 40
• Pressure cooker time saving: water boils at 121°C inside (15 psi gauge) instead of 100°C – cuts cooking time 50-70%

Limitations & notes

Doesn’t include specialized industrial units like ksi (kilopound per square inch), MPa for material strength testing, or vacuum-specific scales (millitorr, micron). For exotic pressure measurements (electrochemistry, fluid dynamics modeling), use specialized engineering calculators. The standard atmosphere value (101,325 Pa) is defined – actual sea-level atmospheric pressure varies with weather.

Frequently Asked Questions

What’s the difference between gauge and absolute pressure?

Absolute pressure: measured from perfect vacuum (0 Pa). Includes atmospheric pressure. Gauge pressure: measured above atmospheric pressure. Tire pressure gauges show GAUGE pressure – your 32 psi tire actually has 32 + 14.7 = 46.7 psi absolute. Pressure cookers and pneumatics also use gauge.

Why is blood pressure in mmHg?

Historical – the original mercury sphygmomanometer measured the height (in mm) of a mercury column the heart could push up. 120 mmHg means the systolic pressure could lift mercury 120 mm. Modern digital monitors still display in mmHg for medical convention continuity.

What tire pressure should I use?

Check your car’s door jamb sticker (driver side) – that’s the recommended cold PSI for stock tires. NOT the max PSI on the tire sidewall (that’s an upper limit). Typically: cars 30-35 psi, SUVs 32-38 psi, trucks 35-40 psi. Adjust slightly down for comfort, up for fuel efficiency.

How does altitude affect pressure?

Air pressure decreases ~12% per 1000m altitude. At 5,500m (Mount Everest base camp), pressure is half sea level. At 8,850m (summit), only 33%. Why climbers use oxygen tanks above 8,000m and why airplane cabins are pressurized.

Why does cooking take longer at altitude?

Water boils at lower temperatures with lower pressure. At sea level: 100°C. At 2,000m altitude: 93°C. At 5,000m: 84°C. Food cooks more slowly because water can’t get hot enough. Pressure cookers solve this by maintaining elevated internal pressure regardless of altitude.

Is 1 bar exactly 1 atmosphere?

Very close but not exactly. 1 atm = 101,325 Pa. 1 bar = 100,000 Pa. So 1 atm = 1.01325 bar. The difference (1.3%) matters for scientific work but is negligible for everyday use – ‘about 1 bar’ is interchangeable with ‘1 atm’ colloquially.

What pressure crushes the deepest fish?

Snailfish living at 8,000m depth experience ~800 atm = 81 MPa = 11,750 psi. Their bodies are adapted – mostly water and gelatinous tissues that don’t compress. At even greater depths (deeper than ~8,200m), the pressure exceeds what proteins can handle – apparent depth limit for vertebrate life.

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