Atmospheres to Pounds per Square Inch

Atmospheres and pounds per square inch

The standard atmosphere is defined as exactly 101,325 pascals, the average air pressure at sea level. Chemistry, diving depth (1 atm per 10 m of water) and gas laws use atmospheres.

One psi is the pressure of one pound-force on one square inch: about 6,894.757 pascals, derived from exact definitions. Tire pressure in the US and UK, air compressors, pressure washers and plumbing use psi.

Worked example

Convert 3 atm: 3 × 14.69594878 = 44.08784633, so 3 atmospheres is 44.08784633 pounds per square inch. Likewise 2 atm = 29.39189755 psi.

Estimating in your head

Multiply by 15 for a quick figure; it is off by about 2.1%. For 3 atm that gives 45 psi, against 44.0878 exactly.

Going the other way

To convert pounds per square inch to atmospheres, divide by 14.69594878 (or multiply by 0.0680459639099). The swap button between the boxes opens that page.

psi = atm × 14.69594878

1 atm = 101,325 Pa and 1 psi = ≈ 6,894.757293 Pa, both by definition, so the factor is their ratio: 14.69594878 (rounded here; the page uses the full value). Results drop binary floating-point noise beyond 15 significant digits and display at the precision you choose (6 significant figures by default). Copy result copies the full value.