Work out how much antifreeze concentrate and water your cooling system needs for a given level of frost protection. Enter your system capacity and the lowest temperature you want to cover.
Coolant / Antifreeze Mix Calculator
Based on typical ethylene-glycol concentrate (protection ≈ 33%→−18°C, 40%→−25°C, 50%→−37°C, 60%→−52°C). Below about −52°C more glycol won't help — that's the practical limit. Never exceed ~70% glycol (it actually protects less). Always use the coolant type/colour your manufacturer specifies and mix with de-ionised water.
How antifreeze protection works
Antifreeze (ethylene glycol) lowers the freezing point of the coolant. Typical protection: 33% mix ≈ −18°C, 40% ≈ −25°C, 50% ≈ −37°C, 60% ≈ −52°C. Below about −52°C, adding more glycol doesn’t help — and above ~70% it actually protects less and cools worse. A 50/50 mix is the usual all-round choice in most climates.
Important
Always use the coolant type/specification your manufacturer lists (OAT, HOAT, IAT — often colour-coded) and don’t mix incompatible types. Use de-ionised or distilled water, never hard tap water. These figures are a planning guide; the exact protection of your specific product is on its label.
Frequently asked questions
What ratio of antifreeze to water do I need?
For most climates a 50/50 mix (≈−37°C protection) is standard. The calculator gives the exact litres for your system size and target temperature.
Can I use ready-mixed coolant?
Yes — ready-mixed (pre-diluted 50/50) coolant goes straight in with no water added, and protects to about −37°C.
Is more antifreeze always better?
No. Past about 60–70% glycol the freeze protection and heat transfer both get worse. Don’t run neat concentrate.