Boyle's Law Calculator
Enter a starting pressure and volume plus the new volume to get the final pressure of a gas held at constant temperature — and see why squeezing a gas pushes its pressure up.
Pressure from a volume change
Enter the initial pressure, initial volume, and final volume and the calculator returns the final pressure using P₁V₁ = P₂V₂.
Keep units consistent
Use the same pressure unit for the answer as the one you type in, and the same volume unit for both volumes. Temperature is held constant.
What is Boyle's law?
Pressure and volume at constant temperature
This Boyle's law calculator describes how the pressure of a fixed amount of gas changes when its volume changes at constant temperature. Boyle's law states that pressure and volume are inversely proportional: squeeze a gas into half the space and its pressure doubles. Written as an equation, the product of pressure and volume stays the same before and after the change, so P₁V₁ = P₂V₂. Enter the initial pressure, the initial volume, and the new (final) volume, and the tool returns the final pressure in whatever pressure unit you used. It is the relationship behind a syringe, a bicycle pump, and the air in your lungs.
Enter the initial pressure and volume plus the final volume to get the final pressure instantly — units are yours to choose, just keep them consistent.
Because the product of pressure and volume is constant, rearranging P₁V₁ = P₂V₂ gives the final pressure directly: multiply the initial pressure by the initial volume, then divide by the final volume.
P₂ = (P₁ × V₁) ÷ V₂Suppose a gas starts at a pressure of 100 (in any unit) filling a volume of 2, and you compress it into a volume of 1. Multiply the initial pressure by the initial volume to get 100 × 2 = 200, then divide by the final volume: 200 ÷ 1 = 200. The pressure has doubled because the volume was halved — exactly the inverse relationship Boyle's law predicts. The answer comes back in the same pressure unit you started with.
The formula is exact for an ideal gas, but a couple of practical points are worth keeping in mind.
Constant temperature, consistent units, ideal gas
Boyle's law holds only while the temperature and the amount of gas stay fixed — if the gas heats up or cools down as you compress it, you need the combined or ideal gas law instead. Keep your units consistent: the final pressure comes back in the same unit as the initial pressure, and both volumes must share one unit. Real gases deviate from the ideal model at very high pressures or very low temperatures, where intermolecular forces start to matter.