Pounds per Square Inch Calculator
Find pressure in pounds per square inch from a force and an area, convert it to metric units, and tell gauge from absolute readings.
🛞 What is Pounds per Square Inch (PSI)?
Pounds per square inch, written psi, is a unit of pressure equal to one pound-force pushing on one square inch of surface. It is the everyday pressure unit in the United States, used for car and bicycle tires, air compressors, scuba cylinders, water supply, hydraulics and pressure washers. Since pressure is force divided by area, the same formula P = F / A works in any unit system. Psi simply uses the pound-force for the force and the square inch for the area, and one psi works out to 6894.757 pascals, or about 6.895 kPa. The Wikipedia article on psi lists the multiples and the other pressure units that go with it.
This calculator is built around psi and its conversions. In Force and area mode it takes a force in lbf, newtons or kilogram-force and an area in square inches, centimetres, millimetres, feet or metres, and returns the pressure in psi with the metric equivalents. In Convert units mode it translates any of nine pressure units into psi, kPa, MPa, Pa, bar, atm, mmHg, inHg and kgf/cm². In Gauge and absolute mode it adds or subtracts the atmosphere, which is the step people most often get wrong when the label says psig or psia.
The gauge versus absolute distinction deserves care. A tire gauge reads the pressure above the surrounding air, so a flat tire reads zero while still holding air at one atmosphere. Absolute pressure is measured from a perfect vacuum, so the same flat tire is about 14.7 psia. The equations of gases, such as the ideal gas law, need absolute pressure, while hose ratings, tire placards and compressor dials use gauge. Typical uses are checking a tire placard against a gauge in kPa, sizing a cylinder for a given load, reading a European manual that quotes bar, and converting a hydraulic press rating from tons on a ram to pressure.
For other forms of the pressure equation, including hydrostatic pressure from depth and solving for force or area, use the pressure calculator. To turn a mass into a force before dividing by area, see the kg to newtons calculator, and for piston and cylinder loads try the piston force calculator.
📐 Formula
📖 How to Use This Calculator
Steps
💡 Example Calculations
Example 1 — A Press Load
A 1500 lbf load acting on a piston face of 12.5 in²
Example 2 — A Tire Pressure in kPa and bar
A tire placard reads 32 psi
Example 3 — Gauge to Absolute for a Tire
A tire reads 35 psig at sea level with the atmosphere at 14.696 psi
Example 4 — SI Units: Newtons on Square Centimetres
A force of 800 N pressing on a contact patch of 4 cm²
Example 5 — Absolute to Gauge in a Vessel
A vessel is at 20 psia and the atmosphere is 14.696 psi
❓ Frequently Asked Questions
🔗 Related Calculators
How do you calculate psi?
Divide the force in pounds-force by the area in square inches. A 1500 lbf load spread over 12.5 square inches produces 1500 / 12.5 = 120 psi. If the force is in newtons and the area in cm squared, convert first or pick those units in the calculator.
What does psi stand for?
PSI stands for pounds-force per square inch, the pressure produced by a force of one pound-force acting on one square inch. It is the standard pressure unit in US customary units.
How many kPa is 1 psi?
One psi is 6.894757 kPa, about 6.895 kPa. Going the other way, 1 kPa is 0.14504 psi. A tire at 32 psi is 220.6 kPa.
How do you convert psi to bar?
Multiply by 0.0689476, or divide by 14.5038. So 32 psi is 2.206 bar and 100 psi is 6.895 bar.
What is the difference between psig and psia?
Psig is gauge pressure measured relative to the surrounding atmosphere, and psia is absolute pressure measured against a perfect vacuum. psia = psig + atmospheric pressure, which is 14.696 psi at standard sea level.
What is a normal car tire pressure in psi?
Most passenger cars call for roughly 30 to 35 psi gauge when the tires are cold, but the correct value is on the placard in the door jamb or in the owner's manual. 35 psig is 49.7 psia and 241 kPa gauge.
How many psi is one atmosphere?
One standard atmosphere is 101325 Pa, which equals 14.6959 psi. Weather and altitude change the actual local value.
How do you convert psi to mmHg?
Multiply psi by 51.715. For example 1 psi is 51.7 mmHg, and 14.696 psi is 760 mmHg, the standard atmosphere. Blood pressure is quoted in mmHg for historical reasons.
Why does pressure go up when the area gets smaller?
Pressure is force per unit area, so a fixed force concentrated on a smaller patch means more force on each square inch. This is why a needle pierces skin and a snowshoe keeps you on the snow.
What is ksi?
Ksi is a kilopound per square inch, 1000 psi. It is used for material strength, so a steel with a yield strength of 50 ksi yields at 50000 psi, or about 345 MPa.
Can pressure be negative?
Gauge pressure can be negative, which indicates a partial vacuum below the atmosphere. Absolute pressure cannot go below zero, so the lowest possible gauge reading is minus the atmospheric pressure.