Pressure Calculator
Solve P = F ÷ A for pressure, force, or area — with kPa and atm equivalents.
Pressure equivalents are shown below in kilopascals and atmospheres.
Pressure is P = F ÷ A — force divided by the area it acts on. A 100 N force spread over 2 m² gives P = 100 ÷ 2 = 50 Pa (50 pascals). Rearrange to F = P × A or A = F ÷ P to find a missing force or area instead.
How pressure works
Pressure measures how concentrated a force is: the same push spread over a small area produces far more pressure than over a large one. That is why a sharp knife or a thumbtack cuts so easily — a modest force is squeezed onto a tiny contact area, so P = F ÷ A shoots up. The SI unit is the pascal (Pa), equal to one newton per square metre (1 Pa = 1 N/m²).
P = pressure (Pa), F = force (N), A = area (m²)
Worked example
A 100 N force presses evenly on a flat plate of area 2 m². Find the pressure, then convert it:
- 1 Write the formula. Pressure equals force divided by area: P = F ÷ A.
- 2 Substitute the values. P = 100 N ÷ 2 m² = 50 Pa.
- 3 Convert to kilopascals. Divide pascals by 1000: 50 Pa ÷ 1000 = 0.05 kPa.
- 4 Convert to atmospheres. Divide pascals by 101325: 50 Pa ÷ 101325 ≈ 0.000493 atm.
Pressure units and everyday reference points
One pascal is a very small unit, so real-world pressures are usually quoted in kPa or atm.
| Quantity | Value | Notes |
|---|---|---|
| 1 pascal (Pa) | 1 N/m² | The SI base unit of pressure |
| 1 kilopascal (kPa) | 1000 Pa | Common for tyres and weather |
| 1 atmosphere (atm) | 101 325 Pa | Standard air pressure at sea level |
| 1 bar | 100 000 Pa | ≈ 0.987 atm; close to one atmosphere |
| Car tyre | ≈ 220 kPa | Roughly 2.2 atm (≈ 32 psi) |
Units, scope, and common mistakes
Keep area in square metres. A force in newtons over an area in cm² will not give pascals — convert first (1 m² = 10 000 cm²). Mixing the two is the most common slip.
Force must be perpendicular. P = F ÷ A uses the component of force acting at right angles to the surface. For a force at an angle, take only its perpendicular part before dividing.
This is mechanical (contact) pressure. The same formula underlies fluid and gas pressure, but buoyancy, depth, and temperature add extra terms there — use the matching fluid equation when a column of liquid or a gas law is involved.