Dokar Henry wata ka’ida ce a cikin ilmin sunadarai da ta bayyana cewa adadin iskar gas da ke narkewa a cikin ruwa ya yi daidai da wani bangare na matsin iskar da ke sama da ruwan. A wasu kalmomi, mafi girman ɓangaren ɓangaren iskar gas sama da ruwa, yawancin gas ɗin zai narke a cikin ruwa. Ana amfani da Dokar Henry sau da yawa don ƙididdige narkewar iskar gas a cikin ruwaye, kuma tana da aikace-aikace masu amfani da yawa a fannoni kamar kimiyyar muhalli, sunadarai na masana'antu, da injiniyanci. An ba wa dokar suna bayan wani ɗan ƙasar Ingila mai suna William Henry, wanda ya fara bayyana ta a shekara ta 1803.