About Pressure Unit Converter — psi, bar, kPa, MPa, atm & More
The pressure unit converter translates a pressure between the units engineering actually mixes on one job: psi and ksi from US datasheets, bar and kPa/MPa from European and SI documents, standard atmospheres from reference conditions, Torr (mmHg) from vacuum work, inches of water from HVAC gauge readings, and kgf/cm² from older metric equipment plates. Every conversion runs through the SI base unit — the pascal — using the factors published in NIST SP 811 Appendix B, so a chain like psi → bar → psi returns exactly where it started.
The anchors worth memorizing: 1 psi = 6,894.757 Pa, 1 bar = 100 kPa exactly (so 1 bar ≈ 14.5038 psi), and 1 standard atmosphere = 101,325 Pa exactly ≈ 14.6959 psi ≈ 1.01325 bar. Because bar and atm sit within 1.3% of each other they get swapped casually in conversation — but not in calculations, and the converter keeps them distinct. Negative inputs are accepted on purpose: a gauge reading below atmospheric (a vacuum-side measurement) is a legitimate negative pressure.
How It Works
- Enter the pressure value, pick the unit it is currently in ("from"), and pick the unit you need ("to"). The headline shows the converted value; the table below it shows the same pressure in all ten units at once, so you can lift whichever one the next document needs.
- Every conversion is value × (pascals per from-unit) ÷ (pascals per to-unit). The factors are the NIST SP 811 Appendix B values — bar, atm, and kgf/cm² are exact by definition; psi and Torr are the published 7-significant-figure values.
- Displayed values are rounded to 6 significant digits. That is display rounding only — the underlying conversion is done in full double precision, which is why round-trips return your original number.
- Watch the gauge-vs-absolute distinction: this tool converts units, it does not add or remove the atmosphere. A 30 psi gauge (psig) reading is 30 + 14.696 = 44.696 psi absolute (psia) at sea level; convert whichever basis you are working in, but keep the basis consistent.
Worked Example
A US pump curve gives a shutoff head of 100 psi, and the European spec sheet wants bar. Through the pascal: 100 psi × 6,894.757 Pa/psi = 689,475.7 Pa, and 689,475.7 ÷ 100,000 Pa/bar = 6.89476 bar — the table's "100 psi" row. The same pressure is 689.476 kPa and 6.8046 atm; note it is under 0.69 MPa, comfortably inside a PN10 (10 bar) flange rating.
psi to bar conversion chart (with kPa and atm)
Common psi values converted to bar, kilopascals, and standard atmospheres with the NIST SP 811 factors (1 psi = 6,894.757 Pa), shown to 6 significant digits — exactly what the converter outputs for the same inputs.
| Pressure | bar | kPa | atm |
|---|---|---|---|
| 1 psi | 0.0689476 | 6.89476 | 0.068046 |
| 10 psi | 0.689476 | 68.9476 | 0.68046 |
| 14.7 psi (≈1 atm) | 1.01353 | 101.353 | 1.00028 |
| 30 psi (car tire) | 2.06843 | 206.843 | 2.04138 |
| 100 psi | 6.89476 | 689.476 | 6.8046 |
| 150 psi (shop air max) | 10.3421 | 1,034.21 | 10.2069 |
Formulas
- Conversion through the base unit
x = value × f_from ÷ f_to- Pascals per unit (the factor table)
psi 6,894.757 · ksi 6.894757×10⁶ · bar 10⁵ · atm 101,325 · Torr 133.3224 · inH₂O 249.082 · kgf/cm² 98,066.5- The everyday anchors
1 bar ≈ 14.5038 psi; 1 atm ≈ 14.6959 psi ≈ 1.01325 bar
Standards & References
- NIST SP 811, Guide for the Use of the International System of Units, Appendix B — conversion factors (psi 6.894757×10³ Pa; Torr 1.333224×10² Pa; inch of water at 39.2 °F 2.49082×10² Pa)
- Exact definitions: 1 bar = 10⁵ Pa; 1 standard atmosphere = 101,325 Pa; 1 kgf/cm² = 98,066.5 Pa
- Displayed to 6 significant digits; conversions computed in full double precision
Frequently Asked Questions
How do I convert psi to bar?
Multiply psi by 0.0689476 (that is 6,894.757 Pa per psi divided by 100,000 Pa per bar). So 30 psi ≈ 2.068 bar and 100 psi ≈ 6.895 bar. Going the other way, multiply bar by 14.5038 to get psi.
Is 1 bar the same as 1 atmosphere?
No — close, but not equal. 1 bar = 100,000 Pa exactly, while 1 standard atmosphere = 101,325 Pa exactly, so 1 atm = 1.01325 bar ≈ 14.696 psi versus 14.504 psi for a bar. The 1.3% gap is harmless in conversation and fatal in a calibration record, which is why the converter treats them as distinct units.
Why does the converter accept negative pressures?
Because gauge pressure is measured relative to the atmosphere, and readings below atmospheric are negative by convention — a vacuum line pulling 5 psi below ambient reads −5 psig. The unit conversion itself is the same multiplication either way. What the tool does not do is convert between gauge and absolute bases; add the local atmospheric pressure (≈14.696 psi at sea level) yourself when you need psia from psig.
What is the difference between Torr and mmHg?
For engineering purposes they are the same size: NIST SP 811 lists both the Torr and the conventional millimeter of mercury (0 °C) at 133.3224 Pa, and vacuum equipment uses them interchangeably. Strictly, the Torr is defined as 1/760 of a standard atmosphere (101,325 ÷ 760 = 133.3224 Pa), which is why 1 atm converts to almost exactly 760 Torr in the result table.
Where does kgf/cm² still show up, and how big is it?
On nameplates of older metric equipment, Japanese and Russian pressure gauges, and some hydraulic documentation. 1 kgf/cm² = 98,066.5 Pa exactly (one kilogram-force on one square centimeter), which is 0.980665 bar ≈ 14.223 psi — about 2% below one bar. Treating kgf/cm² as "basically a bar" is usually the intent of the original designer, but the converter gives you the exact number.