Atmospheres to PSI Converter
Common Conversions
| atm | psi |
|---|---|
| 0.1 | 1.47 |
| 0.5 | 7.348 |
| 1 | 14.696 |
| 2 | 29.392 |
| 5 | 73.48 |
| 10 | 146.96 |
| 20 | 293.92 |
| 50 | 734.8 |
| 100 | 1469.6 |
| 150 | 2204.4 |
| 200 | 2939.2 |
Why this conversion matters in chemistry
Of all the pressure units a chemist runs into, psi is the only one defined directly through force per unit area — pounds of force on a square inch of gauge face — rather than through a fluid column or a coherent SI definition. A fresh nitrogen cylinder delivered at about 150 atm reads something like 2200 psi on the regulator, which is worth knowing when sizing a gas manifold or estimating how long a cylinder will last at a given flow. High-pressure hydrogenations and supercritical-fluid work routinely run at hundreds of atm, where the psi number on the gauge starts looking large and the conversion to atm becomes the thing that keeps a PV = nRT calculation honest.
Formula
Where the factor comes from
Alone in this family, the psi is built from a force over an area rather than from a pascal count or a fluid column, and every ingredient has been exactly defined since the 1959 international yard and pound agreement. The avoirdupois pound is exactly 0.45359237 kg and standard gravity is exactly 9.80665 m/s², so a pound-force is exactly 4.4482216152605 N. A square inch is (0.0254 m)², or exactly 6.4516 × 10⁻⁴ m². Dividing one by the other gives 1 psi = 6894.757293 Pa, and then 101325 ÷ 6894.757293 = 14.6959488 psi per atmosphere. Every input is exact, yet the quotient never terminates — so unlike the bar or kilopascal factors, the number you write down is always a rounded rendering of an exact ratio.
Precision and significant figures
14.69594877551… runs on indefinitely despite being assembled entirely from exact quantities. The customary 14.696 is good to three parts per million, far past anything a laboratory gauge resolves. The habitual 14.7 costs 0.028 percent, invisible on a single reading but worth six-tenths of a psi once scaled to a 150 atm cylinder. Bourdon dials, which is what most regulators carry, are usually specified as a percentage of full scale rather than of reading — so a 3000 psi face rated at two percent is uncertain by sixty psi everywhere on the dial, including down where the needle is showing 50.
Worked Examples
Standard atmospheric pressure — the baseline on any sea-level pressure gauge.
The typical delivered pressure of a full compressed-gas cylinder of nitrogen or argon.
A modest vacuum, still within reach of a water aspirator at the tap.
The kind of pressure a sealed hydrogenation reactor runs at for a high-pressure reduction.
Common mistakes
Gauge pressure hurts most at low readings
Adding 14.696 to convert psig to absolute is routine, and skipping it does the most damage where the numbers are small. A regulator delivering 2 psig is at 16.7 psia — treat that 2 as absolute in a gas-law calculation and you are off by more than a factor of eight, not by the modest 14.7 that intuition suggests.
Two gauges on a two-stage regulator
The high-side dial reports what remains in the cylinder; the low-side reports delivery pressure into the line. They differ by roughly two orders of magnitude, and only one of them belongs in whatever you are calculating. Converting the wrong dial to atmospheres quietly misjudges both flow duration and reaction pressure.
HPLC backpressure reported in psi or bar
Chromatography systems display backpressure in psi in some regions and bar in others, and column pressure limits get published both ways. A 400 bar limit is about 5800 psi; reading a psi figure against a bar-denominated limit, or the reverse, misjudges the remaining margin by a factor near 14.5.