Pressure Converter — PSI, Bar, kPa and More

Q: How many psi are in a bar?

14.5038 psi. Going the other way, 1 psi is 0.0689476 bar. A bar is defined as exactly 100,000 pascals, which makes it a round metric number and a slightly awkward imperial one.

Q: How do I convert psi to kPa?

Multiply by 6.894757. So 100 psi is 689.48 kPa, 3,000 psi of hydraulic pressure is 20.68 MPa, and 90 psi on an air line is 620.5 kPa. To go back, divide by 6.894757 or multiply by 0.145038.

Q: What is the difference between psi, psig and psia?

Psig is gauge pressure, measured relative to the air around the instrument, and it is what almost every dial, sensor and rating on a jobsite reports. Psia is absolute pressure, measured from a vacuum. At sea level, psia is roughly psig plus 14.696. Plain "psi" on a US drawing or nameplate nearly always means psig, but nearly always is not a specification — if the number matters, confirm which one is meant.

Q: Why does OSHA give acetylene two different pressure limits?

Because one of them stops working inside a pressurized space. 29 CFR 1910.253(a)(2) caps acetylene at 15 psig and, separately, at 30 psia. In open air the two are the same rule. Inside a caisson, a tunnel or any chamber where the surrounding air is above atmospheric, a gauge still reading 15 would mean the acetylene is well past the pressure at which it becomes unstable — so OSHA writes the absolute limit as well and says in the rule itself that this is why.

Q: How many psi is one atmosphere?

14.6959 psi, from the standard atmosphere of exactly 101,325 pascals. That is the number to add to a gauge reading to get absolute pressure at sea level. It drops with elevation — roughly 12.2 psi in Denver, about 10 psi at 10,000 feet — which is a real correction for vacuum work, for pump suction and for anything specified in absolute terms.

Q: Is a bar the same as an atmosphere?

No, and treating them as the same is a 1.3% error. A bar is exactly 100 kPa; a standard atmosphere is 101.325 kPa. On a 3,000 psi hydraulic system that gap is about 40 psi. The units are close enough to be used loosely in conversation and far enough apart to matter on a relief valve setting.

Q: What is kgf/cm² and where will I see it?

Kilograms-force per square centimeter, an older metric pressure unit still printed on Japanese, Korean and some European equipment, gauges and hydraulic charts. It is exactly 98,066.5 pascals, or 14.2233 psi — within 2% of a bar, which is why the two are often mixed up. The modern SI equivalent is the bar or the MPa.

Q: How much pressure is a foot of water?

0.4335 psi per foot at 39.2 °F, so a 100-foot head is about 43.35 psi. Column units are temperature-dependent by definition, because they describe the weight of a column of fluid, and warm water weighs slightly less than cold. NIST publishes the 39.2 °F value used here, which is water at its densest.

One psi is 6.894757 kPa and one bar is 14.5038 psi. Enter a pressure, pick the two units and you get the answer plus every other unit at once. The page also covers the difference that actually causes accidents — gauge pressure against absolute pressure, and why OSHA writes both into the same sentence.

Pressure

Type a decimal or a fraction — 90.5 and 90 1/2 both work.

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Results are estimates for planning purposes. Verify with your supplier, engineer, or a qualified professional before ordering material or performing work.

Gauge or absolute — the one that gets written into rules

A pressure gauge reads zero in open air. It is not measuring nothing; it is measuring the difference between the inside of the vessel and the air around the instrument. That is gauge pressure, written psig. Counting instead from a hard vacuum gives absolute pressure, psia, and at sea level the two are 14.696 psi apart.

Converting units never resolves this. 100 psi is 6.895 bar whether it is gauge or absolute, and the converter above cannot know which you have. What decides it is the instrument and the specification.

OSHA writes both into a single sentence, and the reason is worth reading. 29 CFR 1910.253(a)(2) says acetylene shall not be generated, piped or used above 15 psig (103 kPa gauge) — or 30 psia (206 kPa absolute). In open air those are the same limit. Inside a caisson, a tunnel or any pressurized chamber, the surrounding air is already above atmospheric, so a gauge reading 15 would mean the acetylene had gone well past the pressure at which it becomes unstable. The rule says so in its own text: the absolute limit exists to prevent unsafe use in pressurized chambers.

Practical version: on a US jobsite a bare "psi" on a nameplate, a hose, a regulator or a tool almost always means gauge. Almost always is not a specification. If the number governs a relief setting, a test pressure, a vacuum process or work in a pressurized space, confirm which one is meant before you convert it.

Pressures a jobsite actually deals in

Common working pressures converted to bar and kilopascals, with what each one is
Pressure	psi	bar	kPa
Sea-level atmospherethe gauge-to-absolute offset	14.696	1.013	101.3
OSHA cleaning limit for compressed air1926.302(b)(4), with chip guarding and PPE	< 30	< 2.07	< 207
Typical shop air line	90	6.21	620.5
Passenger tire, cold	32	2.21	220.6
Class 8 truck tire	100	6.89	689.5
Common mobile hydraulic system	3,000	206.8	20,684
Hydro-excavation / water jetting	3,000–10,000	207–689	20,700–68,900

Only the atmosphere and the OSHA limit are fixed values — the atmosphere by definition, the limit by 29 CFR 1926.302(b)(4). The rest are typical figures for orientation, not ratings. Every pressure that governs a piece of equipment comes off that equipment.

Four ways a pressure conversion goes wrong

Treating a bar as an atmosphere. A bar is exactly 100 kPa; an atmosphere is 101.325 kPa. It is a 1.3% error — 40 psi on a 3,000 psi system, which is the sort of margin a relief valve is set inside.
Treating kgf/cm² as a bar. Kilograms-force per square centimeter is 14.2233 psi against a bar's 14.5038 — within 2%, close enough to look like a rounding difference and not be one. It still appears on Japanese and Korean gauges and hydraulic charts.
Mixing psi with psf. Structural loads and wind pressures are usually in pounds per square foot; fluid pressures are per square inch. The factor between them is 144, and confusing them changes the answer by two orders of magnitude.
Ignoring elevation on an absolute figure. The 14.696 psi offset is a sea-level number. Denver is around 12.2 psi, and 10,000 feet is around 10. That correction is real for vacuum work, pump suction and anything specified in absolute terms.

How it's calculated

How the conversion is done: result = pressure × (pascals per from-unit) ÷ (pascals per to-unit)
Everything goes to pascals and back, so no chain of rounded factors can accumulate.
The exact factors: 1 psi = 6,894.757293168 Pa · 1 bar = 100,000 Pa · 1 atm = 101,325 Pa · 1 kgf/cm² = 98,066.5 Pa · 1 torr = 101,325/760 Pa
All exact. The psi follows from the pound-force (exactly 4.448 221 615 260 5 N) divided by the square inch (exactly 0.000 645 16 m²); NIST prints it rounded to 6.894 757 E+03 Pa.
The two conversions worth memorizing: 1 bar = 14.5038 psi · 1 psi = 6.894757 kPa
A bar is close enough to one atmosphere (14.6959 psi) that European equipment ratings and American ones look interchangeable and are not. The gap is 1.3%.
Gauge and absolute: absolute = gauge + local atmospheric pressure · at sea level: psia ≈ psig + 14.696
A gauge reads zero in open air because it is measuring the difference from its surroundings. Absolute pressure counts from a vacuum. OSHA writes both into 1910.253(a)(2): acetylene is limited to 15 psig, and separately to 30 psia so that the rule still bites inside a pressurized caisson or tunnel where the surrounding air is not at 14.7 psi.
Water and mercury columns: 1 ft of water (39.2 °F) = 0.4335 psi · 1 inHg = 0.4912 psi
Column units are only defined at a stated temperature, because the density of the fluid moves with it. NIST publishes water at 39.2 °F and mercury conventional; a different reference temperature gives a slightly different factor.

Frequently asked questions