About this tool
The Coolant / Antifreeze Mix Calculator works out how much concentrated antifreeze and how much water to combine to reach a target glycol concentration in your cooling system, and reports the freeze and boil protection that mix provides. For a target glycol fraction f and a system capacity C, antifreeze = C × f and water = C × (1 − f) — so a 50% mix in a 12-quart system is 6 quarts of each. A 50/50 blend is the common all-round choice.
Protection values come from the standard ethylene-glycol property tables, interpolated between published points: roughly 33% glycol protects to −4 °F, 40% to −12 °F, 50% to −34 °F, 60% to −62 °F, and about 68–70% to −84 °F (going stronger than ~70% actually reduces protection). Boiling point rises with concentration and cap pressure; at a 15 psi cap a 50% mix boils near 265 °F and 60% near 270 °F. Both °F and °C are shown. Protection past about 70% glycol falls off, which is why straight antifreeze is never recommended.
An adjust mode helps when the system is already filled: enter the current and target concentration and it tells you how much mixture to drain and replace with pure antifreeze (to raise it) or water (to lower it). All figures are informational and based on generic ethylene-glycol data — always follow your OEM's specified coolant type and mix. Everything is computed locally in your browser.