PSI to Atmospheres Converter
Common Conversions
| psi | atm |
|---|---|
| 1 | 0.068 |
| 5 | 0.34 |
| 10 | 0.68 |
| 14.696 | 1 |
| 25 | 1.701 |
| 50 | 3.402 |
| 100 | 6.805 |
| 200 | 13.609 |
| 500 | 34.023 |
| 1000 | 68.046 |
| 2000 | 136.092 |
| 2200 | 149.701 |
Why this conversion matters in chemistry
psi is the unit you'll see on most gas regulators and gauges in US labs — a standard nitrogen cylinder reads around 2200 psi when full, a steam autoclave holds about 15 psi gauge to reach 121°C. Chemistry calculations almost always want atm (or kPa) instead, so the conversion is the bridge between what the regulator shows and what the ideal gas law wants. Dividing by 14.696 gives you 2200 psi = 150 atm, or 15 psi = 1 atm gauge (about 2 atm absolute — gauge pressures sit on top of atmospheric). Worth keeping the factor mental; it comes up every time someone hands you a pressure reading and expects a molar quantity back.
Formula
Where the factor comes from
This page divides by 14.696, and it is worth noticing that the divisor is itself already rounded. The chain runs psi to pascals to atmospheres. A pound-force is exactly 4.4482216152605 N, spread over a square inch of exactly 6.4516 × 10⁻⁴ m², giving 6894.757293… Pa; the standard atmosphere is exactly 101325 Pa, a value fixed by international agreement rather than measured. Divide and you get 0.06804596390… atmospheres per psi, or 14.695948775… psi per atmosphere read the other way. Taking the reciprocal of a five-figure 14.696 instead lands 3.5 parts per million low — irrelevant at any bench, but it is the reason two calculators can disagree in the sixth digit and both be defensible.
Precision and significant figures
Four figures cover this pair completely. Using 0.06805 per psi, or dividing by 14.70, moves a 2200 psi cylinder reading by well under a tenth of an atmosphere, and no regulator dial resolves anything close to that. The interesting uncertainty sits in what the psi reading means rather than in the conversion. Cylinder pressure tracks temperature, so the same cylinder reads several percent lower after a night somewhere cold, and at 150 atm nitrogen is far enough from ideal that its compressibility factor departs from unity by a few percent — the moles inside are not proportional to the converted pressure however precisely you convert it.
Worked Examples
The anchor conversion. Sea-level atmospheric pressure by definition, and where most psi-to-atm conversions pivot.
Roughly the absolute pressure a steam autoclave hits during sterilization — enough to push water's boiling point above 120°C.
A full compressed gas cylinder — nitrogen, argon, helium. The number you read off the high-pressure gauge on a regulator.
Moderate elevated pressure, common for benchtop catalytic hydrogenation runs.
Common mistakes
Press gauges read line pressure, not sample pressure
Hydraulic presses, including the small ones used to form pellets for infrared work, are graduated in psi of hydraulic line pressure. What reaches the sample is that figure scaled by the ratio of ram area to die area, often by an order of magnitude. Converting the dial reading gives a perfectly correct pressure in atmospheres — just not the pressure acting on the material.
Differential psi is not a system pressure
Backpressure across a column, or drop across a filter, is quoted in psi and is a difference between two absolute pressures. Converting it to atmospheres is arithmetically fine and the answer is a valid pressure difference, but dropped into PV = nRT as though it were the system pressure it describes nothing. Watch for psid, and for readouts that zero themselves at ambient.
The cylinder number is tied to a temperature
A regulator showing 2200 psi describes the gas as it stands right now. Move the cylinder from a 20 °C lab to a 0 °C dock and the same contents read near 2050 psi, which converts to 139 atm rather than 150. If the converted figure is feeding an inventory or a supply-duration estimate, the temperature it was read at is part of the number.