The katal (symbol: kat) is the SI unit of catalytic activity. It quantifies the rate at which a catalyst (such as an enzyme) converts reactants in a chemical reaction. Specifically, one katal represents the catalytic activity that raises the rate of conversion by one mole per second in a specified assay system.

• Definition: One katal refers to an amount of enzyme that gives a catalysed rate of conversion of one mole per second.
• Practical Use: Since the katal is quite large for most enzymatic reactions, the nanokatal (nkat) is commonly used in practice.
• SI Multiples: The katal has various SI multiples, ranging from femtokatal (fkat) to megakatal (Mkat), depending on the scale of catalytic activity.