Article — PSI Conversion Calculator
PSI conversion calculator: every pressure unit, one place
PSI (pounds per square inch) is the imperial pressure unit defined exactly as 6,894.757293 Pa via the 1959 International Yard and Pound Agreement. One atmosphere equals 14.696 psi, a car tyre runs around 32 psi, and hydraulic systems work at 3,000-10,000 psi. This converter handles all common units instantly.
The pound-force on one square inch is small in metric terms, which is why PSI numbers stay manageable across most engineering domains. The same pressure expressed in Pa would need thousands or millions of pascals just to talk about a coffee machine. PSI remains the working unit across US industries even though the SI base is Pa.
What is PSI?
PSI stands for pounds per square inch. One PSI is the pressure of one pound-force distributed evenly over one square inch of area. Since the pound and the inch both have exact SI equivalents (0.45359237 kg and 25.4 mm respectively), PSI itself has an exact SI value: 6,894.757293168 Pa.
The unit appears almost everywhere imperial measures persist: tyre gauges, water pressure regulators, hydraulic schematics, scuba diving tables, soda canister pressures. In Europe and most engineering documentation the same pressures appear in bar or kPa instead. The conversion is mechanical, but the ratios matter for anyone reading specs across regions.
The standard atmosphere is exactly 101,325 Pa, which works out to 14.6959 psi — almost but not quite 14.7. The American "1 atm = 14.7 psi" rule of thumb is accurate to 0.03%.
PSI to metric pressure units
Every pressure unit converts through Pa. PSI to bar uses the factor 0.0689476 (since 1 bar = 100,000 Pa). PSI to kilopascal multiplies by 6.89476. PSI to megapascal — used in high-pressure work — divides by 145.038. The mmHg conversion is 51.7149, useful when reading blood pressure equipment alongside engineering data.
One quirk: the kg/cm² unit (sometimes called kgf/cm² or "technical atmosphere") differs from real atmospheres by about 3.4%. 1 kg/cm² equals 14.2233 psi while 1 atm equals 14.6959 psi. Don't substitute one for the other on a Japanese hydraulic spec sheet.
Quick mental math: psi × 7 gives kPa within 2% (real factor 6.89). psi ÷ 15 gives bar within 3% (real factor 14.5). Good enough for sanity checks before consulting the precise converter.
PSI to bar and kPa reference
The most common everyday PSI values cover a 1000:1 range. Atmospheric pressure (14.7 psi) sits at one end. Hydraulic systems sit at the other, with car tyres, water mains and pneumatic tools filling the middle. The exact bar and kPa equivalents are worth memorising for the half-dozen pressures you actually meet.
- 1 psi = 6.895 kPa = 0.0689 bar = 51.7 mmHg
- 14.696 psi = 101.325 kPa = 1.013 bar = 1 atmosphere
- 32 psi = 220.6 kPa = 2.21 bar (typical car tyre)
- 50 psi = 344.7 kPa = 3.45 bar (household water main)
- 100 psi = 689.5 kPa = 6.89 bar (pneumatic tool)
- 3000 psi = 20.68 MPa = 206.8 bar (high-pressure hydraulic)
- 10,000 psi = 68.95 MPa = 689.5 bar (waterjet cutting)
Tyre and water pressure in PSI
Car tyre pressure recommendations sit between 28 and 35 psi cold. The number on the door jamb is the manufacturer's spec, not the maximum stamped on the sidewall. Underinflation increases rolling resistance and tyre wear; overinflation reduces grip and ride comfort. Each 10°C drop in temperature lowers tyre pressure by about 1 psi.
Household water pressure typically runs 40-60 psi (2.8-4.1 bar). Below 40 psi showers become weak; above 80 psi seals and pipework start to fail. Most water utility regulators are set in this range automatically. Pressure-reducing valves are required by some plumbing codes when the supply exceeds 80 psi.
Hydraulic PSI systems
Industrial hydraulics work in a much higher PSI band. Low-pressure systems run 300-500 psi (jacks, garage door openers). Medium pressure 1000-2000 psi covers most construction equipment. High pressure 3000-6000 psi is standard for mobile hydraulics — excavators, telehandlers, agricultural machinery. Ultra-high systems can reach 10,000 psi for special tools and waterjets.
Each pressure tier brings different safety considerations. ISO 1436 requires hydraulic hoses to withstand four times the maximum working pressure before bursting. A 5,000 psi rated line is proof-tested at 10,000 psi and rated to burst above 20,000 psi.
A pinhole leak in a 3,000 psi hydraulic line can inject fluid through skin without obvious entry wound. The injected fluid causes severe tissue damage within hours. Never check for leaks with a bare hand — use cardboard at arm's length. Seek surgical evaluation immediately if you suspect injection.
PSIA vs PSIG (absolute vs gauge)
Two PSI conventions exist: PSIA (absolute, measured from a perfect vacuum) and PSIG (gauge, measured relative to ambient atmospheric pressure). The relationship is PSIA = PSIG + 14.696. A tyre gauge showing 32 psi means PSIG; the absolute pressure inside the tyre is 46.7 psia.
Engineering specs usually clarify which is meant. If neither A nor G is appended, assume gauge for tyre, water and HVAC contexts, and absolute for thermodynamics, vacuum chambers and aerospace. Mixing them silently is one of the most common conversion mistakes.
Common PSI conversion mistakes
Three errors dominate. First, confusing PSI with kg/cm² when both look similar on a Japanese pressure gauge — the difference is small but matters for tight tolerances. Second, dropping the 14.696 atmospheric offset when converting between absolute and gauge readings. Third, using the wrong rounding for engineering certificates: regulatory bodies usually require at least 4 significant figures.
PSI and temperature effects
Pressure varies with temperature for any sealed gas. Gay-Lussac's law tells us that at constant volume, pressure is proportional to absolute temperature in Kelvin. A car tyre at 32 psi on a 25°C day reads about 30 psi after a 10°C overnight drop. Always measure cold for accurate comparison to door-jamb specs.
Industrial systems compensate for this with pressure relief valves rated above the maximum expected operating temperature. A pneumatic line designed for 100 psi at room temperature may see 110 psi after a few hours of operation in a 40°C engine compartment. Engineers include 20-30% headroom on PSI ratings for this reason.
For scuba tanks the same effect appears in reverse: a tank filled to 3000 psi at the dive shop (25°C) reads about 2700 psi at depth in cold 5°C water. Tank capacity calculations use the gauge reading at depth, not at the surface, to estimate remaining dive time correctly.