Boyle's Law Calculator
Solve for any one of P₁, V₁, P₂, or V₂ using Boyle's Law, P₁V₁ = P₂V₂, at constant temperature.
Leave exactly one field blank and the calculator finds it from P₁V₁ = P₂V₂ (constant temperature). Use any consistent pressure and volume units.
Pressure 1
1
Volume 1
2
Pressure 2
2
Volume 2
1
How it works
Boyle's Law says that for a fixed amount of gas at constant temperature, pressure and volume trade off inversely: squeeze the volume in half and the pressure doubles. Written as an equation, that's P₁V₁ = P₂V₂ — the product stays the same before and after the change.
Leave one of the four boxes empty and the calculator rearranges the equation to fill it in. Want the new pressure after compressing a gas? Enter the starting pressure and volume plus the new volume, and it returns P₂. The same trick works for any of the four quantities.
Because both sides are a product, only the ratio of your units matters, not the units themselves — atmospheres and liters, or kilopascals and milliliters, all work as long as you're consistent on each side. Just don't change temperature partway, since that breaks the assumption the law depends on.
Frequently asked questions
What units should I use?
Any consistent ones. Use the same pressure unit for P₁ and P₂ and the same volume unit for V₁ and V₂. The answer comes back in whichever units you fed in, since Boyle's Law only cares about the ratios.
Does temperature have to stay constant?
Yes — that's the whole premise. Boyle's Law only holds when temperature and the amount of gas don't change. If temperature shifts too, you'd need the combined gas law or the ideal gas law instead.
Why do pressure and volume move in opposite directions?
Gas molecules bouncing in a smaller space hit the walls more often, raising the pressure. Give them more room and the collisions spread out, so pressure drops. That inverse relationship is exactly what P₁V₁ = P₂V₂ captures.