Coolant Mix Calculator

About this calculator

This calculator works out how much antifreeze concentrate and water to mix for a target coolant ratio, based on the freeze- and boil-point protection curves of ethylene or propylene glycol antifreeze at different concentrations — a standard 50/50 mix protects to roughly −37°C (−34°F), while richer mixes protect against colder temperatures up to a point (pure, undiluted glycol actually protects less than a 60–70% mix, since water is needed for the chemistry to work and for heat transfer). Concentrate is normally sold either pre-mixed at 50/50 or as full-strength, so getting the dilution right matters for both the target ratio and the total volume the cooling system holds.

Mechanics and DIY car owners use this before a coolant flush or top-up to hit the manufacturer-recommended concentration for their climate, since too weak a mix risks freezing damage in winter, and — less intuitively — too strong a mix reduces heat transfer efficiency and can actually raise the freezing point again.