Boyle's Law Calculator
Written by Thierno Sadou Diallo, formula verified per our methodology • Last checked on 9/5/2026
Boyle's law is written P₁ × V₁ = P₂ × V₂ at constant temperature. For a gas at 1 atm occupying 10 L and compressed to 5 L, the final pressure reaches 2 atm.
Explanation
Boyle's law describes how an ideal gas behaves during an isothermal change, meaning at constant temperature: the product of pressure and volume stays unchanged (P₁V₁ = P₂V₂). In practice, if you reduce the volume a gas occupies without changing its temperature, its pressure increases proportionally — and vice versa. This is the principle that explains, for instance, why a capped syringe becomes harder to push as you compress the air inside it. This law is an approximation valid for a gas close to "ideal" behavior (moderate pressures, not-too-extreme temperatures); it departs from reality for real gases under extreme pressure or temperature conditions, where more complete models (the van der Waals equation, for instance) become necessary.
Example: compressing 10 L to 5 L
Inputs
Initial pressure: 1 atm. Initial volume: 10 L. Final volume: 5 L.
Calculation
Final pressure = (1 × 10) ÷ 5 = 10 ÷ 5 = 2 atm.
Result
By compressing the gas by half, its pressure doubles: it goes from 1 atm to 2 atm.
Frequently asked questions
Why does temperature need to stay constant?
Boyle's law specifically describes an isothermal change. If temperature varies at the same time as volume or pressure, you need the full ideal gas law (PV = nRT), which accounts for temperature and the amount of substance.
Does the pressure or volume unit matter?
No, as long as the same pressure unit and the same volume unit are used consistently for both states (before and after). The result is expressed in the same pressure unit entered for the initial pressure.
Does this law work for all gases?
It's a good approximation for most gases under everyday conditions (pressure close to atmospheric, room temperature). It becomes less accurate for real gases under very high pressure or very low temperature, where interactions between molecules are no longer negligible.