My car manual says to inflate tires to 35 psi. What is that in atmospheres?

35 ÷ 14.6959 = 2.38 atm. If your gauge reads in bar, 35 psi ≈ 2.41 bar.

I'm solving a chemistry problem that uses the ideal gas law. My pressure gauge reads 29.4 psi. What value do I use for P?

A gauge reads pressure above the surrounding air, so add atmospheric pressure first: 29.4 + 14.696 = 44.1 psi absolute, and 44.1 ÷ 14.6959 = 3.0 atm. The ideal gas law (PV = nRT) works cleanly when P is absolute and in atm, V in liters, and T in Kelvin; the gas constant R = 0.08206 L·atm/(mol·K).

A pressure vessel specification shows a working pressure of 150 psi. Is that high compared to atmospheric pressure?

150 psi ÷ 14.696 = 10.2 atm, about 10 times atmospheric pressure. If the 150 psi is gauge pressure, the absolute pressure is about 11.2 atm. Check the vessel's code documentation for its rating basis.

What's the difference between gauge pressure (psig) and absolute pressure (psia)?

Gauge pressure is measured relative to atmospheric pressure; absolute pressure adds atmospheric pressure on top. A tire gauge showing 32 psi (psig) means 32 psi above atmosphere, so the absolute pressure is 32 + 14.696 = 46.7 psia = 3.18 atm absolute. Gas law calculations always use absolute pressure.

PSI to Atmospheres (atm) Converter

Enter a value to instantly convert between pressure units.

From

Precision4 dp

1 Pound per Sq. Inch = 0.068 Atmosphere

Key Formulas

Pound per Sq. Inch → Bar

bar = psi × 0.0689476

Bar → Pound per Sq. Inch

psi = bar × 14.5038

Atmosphere → Pound per Sq. Inch

psi = atm × 14.6959

Pound per Sq. Inch → Atmosphere

atm = psi × 0.068046

Formula

atm = psi ÷ 14.6959

PSI (pound-force per square inch) is an inch-pound pressure unit. The atmosphere (atm) is a scientific unit equal to mean air pressure at sea level — roughly 14.7 psi. Scientists and engineers use atm to compare pressures with sea-level air pressure or to calculate gas behavior.

Source: NIST SP 811, Table B.8

Reviewed by the Convert Calc editorial team · Last reviewed: 2026-10-06 · see our methodology

Frequently Asked Questions

Real-World Examples

Standard atmospheric pressure at sea level is defined as 101,325 Pa, about 14.696 psi, so 14.696 psi rounds to 1 atm.

14.696 psi = 1 atm

A car tire gauge reads 32 psi, which converts to 2.177 atm. For an ideal gas law calculation, add atmospheric pressure first: 32 + 14.696 = 46.7 psia, about 3.18 atm.

32 psi = 2.177 atm

A scuba tank is filled to 3,000 psi; a dive instructor teaching gas physics wants students to grasp that this is roughly 204 times the pressure we breathe at the surface.

3000 psi = 204.14 atm

An engineer converts a 100 psi compressor setting to atmospheres for a metric specification.

100 psi = 6.8 atm

psi to bar bar to psi atm to psi kpa to psi psi to kpa

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