Coolant Mix Freeze Protection Calculator

About this calculator

Ethylene glycol antifreeze mixed with water lowers the coolant's freezing point through freezing-point depression, but the relationship isn't linear — a 50/50 mix (by volume) typically protects down to around minus 37°C (minus 34°F), which is close to the maximum practical protection, while pushing the concentration much higher than 60-70% glycol actually raises the freezing point again and reduces heat transfer efficiency, because pure glycol alone freezes at a relatively mild temperature and water is what the glycol needs to depress.

Mechanics and vehicle owners check this ratio before winter or when topping up a cooling system, because using plain water or too weak a mix in a cold climate risks the coolant freezing, expanding, and cracking the engine block or radiator — one of the most catastrophic and expensive failures a cooling system can suffer — while an overly concentrated mix wastes money on glycol and can actually reduce cooling performance in hot weather.

This calculator takes your antifreeze concentration percentage and returns the lowest temperature your coolant mix protects against, so you can confirm it's adequate for your climate.