Pressure Converter

Pressure Converter

This pressure converter transforms values between eight common units: PSI, bar, atmospheres (atm), kilopascals (kPa), pascals (Pa), millimeters of mercury (mmHg), torr, and inches of mercury (inHg). Pressure shows up in more daily contexts than most people realize — tire gauges, weather apps, blood pressure cuffs, hydraulic lines, and scuba equipment all use different units. Getting the conversion wrong can mean underinflated tires, a misread weather report, or a misunderstood medical reading. This tool eliminates that confusion with instant, accurate conversions across all eight units.

How Pressure Conversion Works

All conversions route through the pascal (Pa) as the SI base unit. The input is multiplied by its source factor to produce pascals, then divided by the target unit’s factor to get the result.

Key conversion factors to pascals:

• 1 PSI = 6,894.76 Pa
• 1 bar = 100,000 Pa
• 1 atm = 101,325 Pa
• 1 kPa = 1,000 Pa
• 1 mmHg = 133.322 Pa
• 1 torr = 133.322 Pa
• 1 inHg = 3,386.39 Pa

Example formula — PSI to bar: PSI × 6,894.76 = Pa, then Pa ÷ 100,000 = bar Shortcut: PSI ÷ 14.504 = bar

Worked Examples

A driver checks his tire pressure with a US gauge reading 34 PSI, but his car’s door-jamb sticker was printed in bar for a European market. Converting: 34 ÷ 14.504 = 2.34 bar. The manufacturer spec is 2.3 bar, so the tire is within 0.04 bar — close enough. He tops off slightly and moves on.

A weather enthusiast in Chicago reads a barometric pressure of 29.85 inHg on her analog barometer and wants to compare it to the 1008.8 hPa reading on a digital station she just bought. Converting: 29.85 inHg × 3,386.39 = 101,085 Pa = 1010.9 hPa. The two readings differ by 2.1 hPa, which is within calibration tolerance for a consumer barometer.

A mechanical engineer is specifying a hydraulic system that must operate at 3,000 PSI. The European supplier quotes maximum working pressure in bar. Converting: 3,000 ÷ 14.504 = 206.8 bar. The supplier’s 210-bar rated fitting has adequate margin, so the engineer approves the part.

Expanded Reference Table

When to Use This Converter

• Automotive maintenance — US tire gauges read PSI; European cars often spec pressure in bar; use this converter to cross-reference without guessing
• Medical readings — blood pressure is measured in mmHg in the US but sometimes reported in kPa on international health records; a reading of 120/80 mmHg = 16.0/10.7 kPa
• Weather monitoring — US weather apps use inHg; international forecasts use hPa (= mbar); 29.92 inHg = 1013.25 hPa at sea level
• Scuba and altitude planning — pressure increases by roughly 1 atm (14.7 PSI) for every 10 meters underwater; use this converter to calculate absolute pressure at depth
• Industrial and hydraulic systems — supplier specs from different countries use bar or kPa while US equipment ratings are in PSI; convert before selecting fittings or relief valves

Common Mistakes to Avoid

1. Confusing gauge pressure with absolute pressure — PSI gauge (PSIG) reads zero at atmospheric pressure, while PSI absolute (PSIA) includes the 14.696 PSI of atmosphere. A tire gauge reading of 32 PSIG is actually 46.7 PSIA. Most converters, including this one, work with absolute values — add 14.696 to a PSIG reading before converting if the target application needs absolute pressure.
2. Treating bar and atm as equal — 1 bar = 100,000 Pa and 1 atm = 101,325 Pa, a 1.3% difference. At high pressures (e.g., 200 bar vs. 200 atm), this becomes a 2.65 bar (38 PSI) discrepancy — enough to matter in a pressure vessel rating.
3. Using mmHg and torr interchangeably without checking — they are numerically identical for most practical purposes (1 mmHg = 1.000 torr at 0°C), but torr is defined relative to atm (1 torr = 1/760 atm) while mmHg is defined by mercury column physics. For precision lab work, verify which unit the specification requires.
4. Forgetting altitude effects — standard pressure (1 atm) applies at sea level. At 5,000 feet elevation, atmospheric pressure is about 12.2 PSI (0.83 atm). Any application that references “standard” pressure — calibrating instruments, interpreting vacuum specs — needs to account for local altitude.

Quick Reference Benchmarks

• Standard sea-level atmosphere: 14.696 PSI = 1 atm = 101.325 kPa = 1013.25 hPa = 29.92 inHg = 760 mmHg
• Typical car tire pressure: 30-35 PSI = 2.07-2.41 bar = 207-241 kPa
• Normal blood pressure (systolic): 120 mmHg = 16.0 kPa = 2.32 PSI
• SCUBA at 10 m depth: 2 atm absolute = 29.4 PSI absolute = 202.65 kPa
• A strong storm low pressure: ~28.50 inHg = 965 hPa (vs. standard 29.92 inHg)
• Bicycle tire (road): 100-130 PSI = 6.9-9.0 bar

Tips

1. For tire pressure, the quickest mental conversion is PSI ÷ 14.5 = bar. A 33 PSI tire is about 2.28 bar — close enough for inflation purposes before fine-tuning with this calculator.
2. Blood pressure in mmHg can be roughly converted to kPa by dividing by 7.5. So 120/80 mmHg ÷ 7.5 = 16.0/10.7 kPa. This is useful when reading European medical charts.
3. hPa and mbar are numerically identical — if your weather station shows hPa and another shows mbar, no conversion is needed. Both equal 100 Pa.
4. When specifying industrial components internationally, always confirm whether a rating is in gauge or absolute pressure and whether it uses bar or PSI — a 10-bar rated fitting and a 10-PSI rated fitting are not even close (145 PSI vs. 10 PSI).
5. For SCUBA dive planning, add 1 atm (14.696 PSI) for every 10 meters of water depth to get absolute pressure. At 30 meters, a diver experiences 4 atm = 58.8 PSI absolute — a useful check against regulator and tank ratings.
6. Vacuum pressure is often expressed as a negative gauge pressure or as a percentage of atmospheric. A “29 inHg vacuum” means 29 inHg below atmosphere, which equals about 0.03 atm absolute (nearly full vacuum).