The Law of Charles and Gay-Lussac (frequently called simply Charles' Law) is one of the gas laws, and relates the volume and temperature of an ideal gas held at a constant pressure. The law was first published by Joseph Louis Gay-Lussac in 1802, but he referenced unpublished work by Jacques Charles from around 1787. This reference has led to the law being attributed to Charles.

The law, expressed in symbols, is:

<math>\frac{T}{V} = k<math>

where

V is the volume measured in cubic metres;

T is the temperature measured in kelvins;

k is a constant.

To maintain the constant during heating of a gas, at fixed pressure, requires that the volume increase. Conversely, cooling the gas decreases the volume. The exact value of the constant need not be known to make use of the law in comparison between two volumes of gas at equal pressure:

<math>\frac{T_1}{V_1} = \frac{T_2}{V_2} \qquad \mathrm{or} \qquad \frac {T_2}{T_1} = \frac{V_1}{V_2}<math>

See also

• Making Charles' law tubes for instructions on how to make suitable equipment to demonstrate this law in a classroom.

es:Ley de Charles y Gay-Lussac fr:Loi de Gay-Lussac ja:シャルルの法則 pl:Prawo Gay-Lussaca sl:Gay-Lussacov zakon