Pressure Calculator

How to use the pressure calculator

1. Fill in the fields — they start with a worked example.
2. Read the answer, and the arithmetic shown beneath it.
3. Copy the results, or adjust the inputs to compare scenarios.

About this tool

Pressure is force spread over an area, and the area is where it gets interesting. The same force through a smaller contact patch produces a proportionally higher pressure, which is why a stiletto heel can mark a floor a car would not — the load is smaller and the area is very much smaller.

The unit that catches people is the pascal, because it is tiny. One pascal is one newton over one square metre, roughly the pressure of a sheet of paper resting on a table, so real figures are given in kilopascals, bar or megapascals. Atmospheric pressure is about 101 kilopascals, which makes it a useful sanity check: an answer in the tens of thousands of pascals is around atmospheric, and an answer in single pascals means an area entered in the wrong unit.

That is the failure this calculator is built to catch. Areas entered in millimetres when the tool expects metres are out by a factor of a million, and the resulting pressure is out by the same factor — so the units are explicit, and the area is worked out from a diameter or a rectangle rather than left as a number to convert by hand.

Gauge and absolute pressure are worth distinguishing too. A tyre gauge reads the pressure above atmospheric, so a tyre at 2.3 bar gauge holds about 3.3 bar absolute. Both figures are shown, since a specification that does not say which it means is ambiguous.

Common uses

• Working out the pressure a load puts on a surface.
• Converting a force and area into psi for a specification.
• Checking whether a contact pressure is within a material's limit.

Frequently asked questions

How do I calculate pressure?

Divide the force by the area it acts over. A newton spread across a square metre is one pascal, which is a very small pressure — real figures are usually in kilopascals, bar or psi.

What is the difference between gauge and absolute pressure?

Gauge pressure is measured above atmospheric, which is what a tyre gauge shows. Absolute pressure includes the atmosphere, so it is about 101 kPa higher.

Why is my pressure figure enormous?

Almost always an area entered in the wrong unit. Square millimetres against square metres is a factor of a million, and the pressure is wrong by the same factor.