From AMS Glossary
(Also called Charles's law, Gay–Lussac's law.) An empirical generalization that in a gaseous system at constant pressure, the temperature increase and the relative volume increase remain in approximately the same proportion for all so-called perfect gases.
where t is temperature, v is the volume, and c is a coefficient of thermal expansion independent of the particular gas. If the centigrade temperature scale is used and v0 is the volume at 0°C, then the value of the constant c is approximately 1/273.