Dokar Charles wata doka ce ta iskar gas wacce ta bayyana cewa idan aka matsa lamba akai-akai, yawan adadin iskar gas yana daidai da cikakken zafinsa. Ma’ana yayin da zafin iskar gas ke karuwa, haka ma karfinsa ke karuwa, kuma yayin da yanayin zafi ya ragu, haka ma karfinsa ya ragu, matukar karfin ya tsaya cik. An ba wa dokar sunan wani masanin kimiyar Faransa Jacques Charles, wanda ya fara tsara ta a shekara ta 1787.