Pressure formula
P = FA
| Symbol | Quantity | SI unit | Meaning |
|---|---|---|---|
| P | Pressure | Pa | Pressure |
| F | Force | N | Force acting perpendicular to the surface |
| A | Area | m² | Area over which the force is spread |
What is Pressure?
Pressure: Pressure is the force acting perpendicular to a surface divided by the area over which it acts.
Pressure measures how concentrated a force is. The same force on a smaller area gives a higher pressure, which is why knives cut and snowshoes don't sink. The SI unit is the pascal (1 Pa = 1 N/m²).
In gases, pressure comes from molecular collisions with the container walls (see the ideal gas law). Pressure differences drive bulk flow, while concentration differences drive diffusion.
How to use this calculator
- Choose the quantity you want to find in the Calculate menu. It is highlighted as the result field.
- Enter the known values. Scientific notation such as
1.6e-11is accepted. - Select a unit for each value. Units are converted to SI automatically.
- The answer updates as you type. Open Show calculation steps to see the working, or use Copy result to share a link with your inputs.
Worked example
A 70 kg person (≈ 700 N) stands on 250 cm² of shoe sole.
- P = 700 / 0.025 = 28 kPa.
Frequently asked questions
How many pascals are in one atmosphere?
1 atm = 101 325 Pa = 1.01325 bar = 760 mmHg = 14.696 psi.
What is the difference between gauge and absolute pressure?
Absolute pressure is measured from a perfect vacuum. Gauge pressure is measured relative to atmospheric pressure: P_abs = P_gauge + P_atm.