Article — psi to atm Conversion Calculator
psi to atm conversion: tires, scuba tanks, and gas laws
One standard atmosphere equals exactly 14.69594877 psi. To convert psi to atm, divide by 14.696. To convert atm to psi, multiply by 14.696. The factor traces back to the SI definitions of both units in pascals.
Psi is the unit America never gave up. Tire shops, garden hoses, scuba shops, and home compressors all label in pounds per square inch, even as the rest of the world moved to bar and kilopascal. Converting between psi and atmospheres lets you bridge American hardware to international physics and chemistry references.
What is psi to atm conversion?
Psi stands for pounds per square inch, an imperial unit defined as the pressure exerted by one pound-force spread across one square inch of area. One square inch is 6.4516 square centimeters, and one pound-force is 4.448 newtons, which works out to 6,894.757 pascals per psi. The standard atmosphere is exactly 101,325 pascals, so 1 atm equals 14.69594877 psi.
The conversion is exact, not approximate. Both units reduce to a precise pascal value, so the ratio is a defined constant. The figure 14.696 covers four significant digits, which is plenty for almost any practical purpose, but the calculator on this page carries the full eight digits for cases where they matter.
The psi to atm formula
Convert psi to atmospheres by dividing the psi value by 14.696. So 30 psi becomes 2.041 atm, 100 psi becomes 6.805 atm, and a 3,000 psi scuba tank reads 204.1 atm. The reverse formula multiplies atm by 14.696: 1 atm is 14.696 psi, and 4 atm at 30 meters of seawater equals 58.78 psi absolute.
atm = psi / 14.696 psi = atm * 14.6961 atm = 14.696 psi 1 atm = 101.325 kPa1 bar = 14.504 psi 1 atm = 1.01325 barFor mental math, treat 1 atm as 15 psi. The error is 2.07%, fine for sketching a tire-pressure conversion in your head but wrong for instrument calibration. Use 14.696 (or the full 14.69594877) whenever you write something down.
psi to atm in tire pressure
Tire pressure is the most common reason people convert psi to atm. The driver-door placard on a US car lists psi; a European or chemistry-class reference uses atm or bar. A typical sedan recommendation of 32 psi equals 2.178 atm or 2.21 bar. Light trucks at 40 psi run 2.72 atm, and a road bicycle inflated to 100 psi sits at 6.80 atm.
Gauge versus absolute matters for tires. A tire gauge reads pressure above atmospheric, so a 32 psi reading is actually 46.696 psi absolute (gauge plus 14.696 psi of surrounding air). The atm value of 2.178 already includes the gauge convention, because that is the form people care about. For gas-law calculations involving tire air, add 1 atm back in.
The recommended tire pressure on the door placard is cold-tire pressure. After 30 minutes of highway driving, a tire heats up by 25 to 50 degrees F, and the pressure rises by 4 to 6 psi (about 0.3 atm) because gas pressure scales linearly with absolute temperature. Always check tires cold for accurate readings.
psi to atm in scuba diving
Diving works in absolute pressure: the surface contributes 1 atm of air, and every 10 meters of seawater adds another atm. At 30 m the total is 4 atm, or 58.78 psi. Dive computers report depth and pressure together because gas absorption follows Henry's law and depends on partial pressures.
Scuba cylinders are charged to high psi values. The standard aluminum 80 holds 3,000 psi, which is 204.1 atm. Steel cylinders go to 3,442 psi (234.1 atm). Banked nitrox fills can run 4,500 psi (306 atm). At those pressures the ideal gas law starts to break down, so dive shops use real-gas equations when computing exact fill volumes.
A scuba tank filled to 3,000 psi at 70 F will read about 3,200 psi after sitting in a sunny car at 100 F, and about 2,800 psi after a cold morning. The mass of gas inside is the same. Always rate cylinders at the manufacturer test temperature, and never overfill expecting cooling will save you.
psi and atm in pneumatics and HVAC
Workshop air compressors typically supply 90 to 175 psi, which is 6.12 to 11.91 atm. Pneumatic nail guns operate at 70 to 120 psi (4.76 to 8.16 atm). Industrial air systems can reach 200 psi (13.6 atm), and laboratory bottled gases reach 2,000 to 3,000 psi (136 to 204 atm) at full charge.
HVAC technicians sometimes need the atm value for refrigerant pressure-temperature charts published in old chemistry references. R-410A pressure at 100 F is about 300 psi (20.4 atm); R-134A at the same temperature sits at 125 psi (8.5 atm). The atm reading lets you cross-reference any textbook gas-law calculation.
psi vs bar vs kPa vs atm
Four units measure the same thing in different ways. Psi is imperial. Bar is metric but not SI. KPa is SI metric. Atm is the chemistry reference. They all relate by clean factors that are worth committing to memory.
Common psi-to-atm mistakes
Three errors dominate the support tickets pressure-conversion sites receive. The first is rounding 14.696 to 15. The 2.07% error is small for a single tire, but it compounds over multiplication in any gas-law problem. Always carry at least 14.7 in calculations.
The second is mixing bar and atm. They look interchangeable on a dive computer, and 1 bar is close to 1 atm, but the 1.3% difference matters in commercial gas sales and tank certifications. Read the unit label carefully.
The third is forgetting the surface atm in dive calculations. A depth gauge reads zero at the surface but the diver is already at 1 atm absolute. Total pressure at depth equals surface atm plus water atm. A diver at 30 m experiences 4 atm absolute, not 3 atm.
Memorize 14.696 psi = 1 atm = 101.325 kPa = 1.01325 bar = 760 mmHg. Those five values cover every conversion in tire pressure, scuba diving, weather, chemistry, and medical pressure. Any other conversion can be derived from these.
Quick reference values
Psi values span everyday tire pressures up to extreme industrial and dive cylinder pressures. The conversions to atm are linear, but the order-of-magnitude difference between scenarios is worth noting.
- Sea level = 14.696 psi = 1 atm
- Bike tire (road) = 100 psi = 6.80 atm
- Car tire (sedan) = 32 psi = 2.18 atm
- Truck tire = 80 psi = 5.44 atm
- Dive at 10 m = 29.39 psi = 2 atm absolute
- Dive at 30 m = 58.78 psi = 4 atm absolute
- Workshop air = 90 psi = 6.12 atm
- Scuba tank (AL80) = 3,000 psi = 204.1 atm
- Hydraulic press = 3,000 to 5,000 psi = 204 to 340 atm
- Industrial gas cylinder = 2,400 psi = 163.3 atm