Article — Kg/cm² to PSI Converter
Kg/cm² to PSI Converter: The Engineering Bridge Between Metric and Imperial Pressure
One kilogram-force per square centimeter (kgf/cm²) equals exactly 14.223343 psi. Both units are now defined in pascals, so the conversion is a fixed constant: 1 kgf/cm² = 98,066.5 Pa and 1 psi = 6,894.757 Pa. A car tire inflated to 2.3 kgf/cm² therefore reads 32.71 psi on a US gauge, and a 150 kgf/cm² hydraulic line carries 2,134 psi.
The kgf/cm² unit is also called the technical atmosphere (symbol at), and despite SI moving toward pascals and bar, it still appears on legacy Japanese tire-pressure stickers, German hydraulic pumps and Eastern European refrigeration plates. PSI continues as the dominant pressure unit in the US, UK and most aerospace specifications.
What is kgf/cm² and what is psi?
Kgf/cm² is the force of one kilogram-force applied over one square centimeter. A kilogram-force is the weight of a 1 kg mass at standard gravity, 9.80665 m/s². So one kgf/cm² is one kilogram of weight spread over an area smaller than a US dime. In SI base units that comes out to exactly 98,066.5 pascals.
PSI, the pound per square inch, is the force of one pound-force on one square inch. One pound-force is defined as 4.4482216 newtons, and one square inch is 6.4516 square centimeters. Multiply through and you get 6,894.757 pascals per psi. Like the kgf/cm² value, that number is a defined constant rather than a measurement.
The kgf/cm² is not officially part of the SI system, but the BIPM accepts it as a non-SI unit for use alongside SI in industry. That is why it still appears in ISO machinery standards even though pascals are technically preferred.
The kgf/cm² to psi conversion factor
Divide 98,066.5 by 6,894.757 and you get 14.223343095213. That is the exact conversion factor from kgf/cm² to psi. The reverse factor is 1 divided by that number, or 0.0703070. Both values are irrational, so any calculator that uses 14.22 instead of the full constant introduces a small rounding error that compounds at higher pressures.
For a tire at 2.3 kgf/cm², the difference between 14.22 and 14.2233 amounts to 0.008 psi, well below the resolution of any gauge. For a hydraulic system at 250 kgf/cm², the same rounding produces a 0.83 psi error, still negligible. For a 700 kgf/cm² high-pressure waterjet, the error reaches 2.3 psi, which starts to matter for safety calculations. Engineering software stores the full constant.
kgf/cm² × 14.22 ≈ psi psi ÷ 14.22 ≈ kgf/cm²kgf/cm² × 14 + kgf/cm²/5 (mental math, 0.3 % off)kgf/cm² ≈ bar (2 % difference)Tire pressure in kgf/cm² and psi
Japanese and older European tire-pressure placards specify pressure in kgf/cm². A Toyota or Honda from the 1990s typically lists 2.2 to 2.4 kgf/cm² on the door jamb, which converts to 31 to 34 psi. Modern cars built after 2000 use bar or kPa on the placard, but the underlying tire still inflates the same way.
Passenger car tires are designed for 2.0 to 2.8 kgf/cm² of cold inflation pressure. Below 1.8 kgf/cm² the sidewall flexes too much, raising rolling resistance and heat. Above 3.2 kgf/cm² the contact patch shrinks, reducing grip and accelerating center-tread wear. The TPMS sensors in modern cars trigger at roughly 25 percent below the placard value, which on a 2.3 kgf/cm² placard is about 1.7 kgf/cm² or 24 psi.
Hydraulics, pneumatics and refrigeration
Industrial hydraulic systems are where kgf/cm² to psi conversion matters most. A mid-sized hydraulic press operates at 150 to 250 kgf/cm² (2,134 to 3,556 psi). Heavy stamping presses and injection-molding machines push to 400 to 600 kgf/cm² (5,689 to 8,534 psi). Excavator hydraulics typically run at 280 to 350 kgf/cm² (3,982 to 4,977 psi).
Pneumatic shop air sits at 6 to 8 kgf/cm² (85 to 114 psi). The standard regulator on a workshop compressor caps at 7 kgf/cm² (99 psi), which feeds pneumatic drills, impact wrenches and paint sprayers. Refrigeration compressors discharge between 15 and 30 kgf/cm² (213 to 426 psi) depending on the refrigerant and ambient temperature.
A relief valve marked 250 kgf/cm² protects a system at 3,556 psi. Reading 250 as psi instead of kgf/cm² produces a relief valve set 14 times too low — the system would never reach operating pressure and the pump would dead-head. Always check the unit symbol on the nameplate before calibration.
Kgf/cm² vs bar, atm and pascal
One kgf/cm² equals 0.980665 bar, 0.96784 standard atmospheres and 98,066.5 pascals. The bar is now the ISO-preferred metric pressure unit, defined as exactly 100,000 Pa. Because 98,066.5 is close to 100,000, kgf/cm² and bar differ by less than 2 percent. Engineers often substitute the two for quick tire reading, but precision instruments and safety calculations require the exact factor.
The standard atmosphere (atm) is 101,325 Pa exactly, defined to match average sea-level air pressure. So 1 atm equals 1.0333 kgf/cm². The pascal itself is one newton per square meter, and one kgf/cm² is 98.0665 kPa or 0.098 MPa. SI Megapascals appear on most modern hydraulic pump nameplates.
- 1 kgf/cm² = 14.2233 psi (exact constant, defined in pascals)
- 1 kgf/cm² = 0.98 bar = 0.97 atm
- 1 kgf/cm² = 98,066.5 Pa = 98.0665 kPa
- 1 psi = 0.0703 kgf/cm² = 6,894.757 Pa
- 1 bar = 14.5038 psi = 1.0197 kgf/cm²
- 1 atm = 14.6959 psi = 1.0333 kgf/cm²
- 1 MPa = 145.038 psi = 10.197 kgf/cm²
Gauge vs absolute pressure
Gauge pressure is measured above atmospheric, absolute pressure is measured above vacuum. Tire gauges, shop air gauges and most industrial pressure indicators read gauge pressure, often marked as g or psig. At sea level, absolute pressure equals gauge pressure plus 1.033 kgf/cm² (or plus 14.696 psi). At altitude, atmospheric pressure drops, so the offset shrinks.
The distinction matters for refrigeration, vacuum systems and HVAC. A vacuum gauge reading negative kgf/cm² indicates pressure below atmospheric — an absolute pressure between zero and 1.033 kgf/cm². Mixing gauge and absolute values in calculations is one of the most common engineering errors.
If a pressure value is below 1 kgf/cm² and described as a vacuum or partial vacuum, it is almost certainly absolute. If the gauge has a needle that rests at zero with the system open to room air, it reads gauge pressure.
Kg/cm² to psi conversion mistakes
The most common mistake is using 14.7 instead of 14.2 for the conversion factor. The number 14.7 is the value of standard atmospheric pressure in psi (rounded from 14.696), not the kgf/cm² to psi factor. Confusing the two produces a 3.4 percent error, which adds up at industrial pressures.
A related error is treating kgf/cm² as bar without correction. The two differ by 2 percent. On a 250 kgf/cm² hydraulic relief valve, that error becomes 5 bar (72.5 psi) of margin lost. For tires the difference is harmless, but for engineering specifications it must be respected.