Coolant Mix Freeze Protection Calculator

How it is calculated

The input Antifreeze concentration is the share of ethylene glycol antifreeze in the mix, by volume, from 0 to 70. The tool does not use a formula; it looks the value up in a table of freezing points and interpolates in a straight line between neighbouring rows:

%: 0 → 0 °C, 10 → -4, 20 → -9, 30 → -16, 40 → -26, 50 → -37, 60 → -52, 70 → -64

Between two rows: T = T₀ + (T₁ − T₀) × (pct − pct₀) ÷ (pct₁ − pct₀). The Fahrenheit value is °C × 9 ÷ 5 + 32. Both are rounded to one decimal. Anything below 0 % or above 70 % gives no result. The figure is the point where the mix starts to freeze for a pure glycol-and-water blend; it is not a safe operating limit, and other glycol types differ.

Common mistakes

• Entering the ratio as antifreeze to water (1:2) instead of the percentage of antifreeze in the total. A 1:2 mix is about 33 %, so type 33.
• Mixing by weight and entering the value as if it were by volume. The table is by volume.
• Entering the water share instead of the glycol share. 40 % water is 60 % antifreeze, which the tool rates at -52.0 °C, not -26.0 °C.
• Assuming more antifreeze is always better. The tool accepts only up to 70 % and treats it as a lookup, so it cannot tell you where a stronger mix stops helping; a richer blend also costs more.
• Treating the result as the lowest safe working temperature. It is the freezing point of the mix; leave a margin below it.