Boyle's Law Pressure-Volume

How it is calculated

Boyle's law says the product of pressure and volume stays constant for a fixed amount of gas at constant temperature: P1 × V1 = P2 × V2. The tool solves for the final pressure: P2 = P1 × V1 ÷ V2. The result is a bare number with no unit attached; it comes out in whatever pressure unit you used for P1 (kPa, atm, bar, psi). Likewise V1 and V2 can be in any volume unit, as long as both use the same one. All three values must be above zero. Use absolute pressure, not gauge pressure, and keep the temperature and the amount of gas unchanged. If the gas leaks, heats or condenses, the law no longer applies.

Common mistakes

• Entering gauge pressure (for example a tyre gauge reading). The law needs absolute pressure, which is gauge plus about 101.3 kPa at sea level.
• Mixing volume units for V1 and V2, such as litres and millilitres.
• Applying the law when the temperature changes. A gas that heats up during compression breaks the assumption.
• Reading the result in the wrong unit. The tool does not label it; it is in the same unit as your P1.
• Swapping V1 and V2 and getting a pressure drop where a rise was expected. Smaller final volume means higher pressure.