Dokar Pascal, wadda kuma aka fi sani da Pascal's Principle, ƙa'idar kimiyya ce a cikin injiniyoyin ruwa waɗanda ke nuna cewa matsa lamba da aka yi wa wani ruwa da ke cikin akwati yana yaɗuwa daidai gwargwado a ko'ina cikin ruwan, ba tare da asarar kuzari ba. Ana kiran wannan ka'ida bayan Blaise Pascal, masanin lissafi kuma masanin kimiyyar lissafi dan kasar Faransa wanda ya fara tsara ta a karni na 17. Ƙa'idar tana da aikace-aikace masu yawa, ciki har da na'urorin lantarki, waɗanda ke dogara ga ka'idar don samarwa da watsa wutar lantarki ta amfani da ruwa, kamar ruwa ko mai.