Combined Gas Law Calculator

This calculator solves the combined gas law, which links the pressure, volume and temperature of a fixed amount of gas as it changes from one state to another. The combined gas law states that pressure times volume divided by temperature stays constant, so the initial pressure times volume over temperature equals the final pressure times volume over temperature. It elegantly rolls together the three classic gas laws: Boyle's law, that pressure and volume are inversely related at constant temperature; Charles's law, that volume is proportional to temperature at constant pressure; and Gay-Lussac's law, relating pressure and temperature. Because it connects a before and after state, it is exactly what you need for the common problem of a gas being compressed, heated or cooled and asking what happens to the remaining quantity. This tool solves for whichever variable you choose. You enter the initial pressure, volume and temperature, the two known values of the final state, and select which final quantity you want to find, and the calculator works it out. It also shows the value of pressure times volume over temperature for both states, which should match, confirming the law holds. Temperature must be in absolute units, kelvin, because the law depends on absolute temperature; using degrees Celsius gives wrong answers, a very common mistake. The results update as you type. Use it for chemistry and physics homework, for gas problems in engineering, or to predict how a gas responds to changing conditions. Pressure and volume can be in any consistent units, since they appear on both sides, as long as you keep them the same throughout. The calculation is rounded for display.

P1V1/T1 = P2V2/T2. Temperature MUST be in kelvin. Pressure and volume can be any units if consistent on both sides. When solving for V2 or P2, T2 is read from its field.