Coolant Mix Calculator
Get the exact antifreeze-to-water ratio for your target freeze protection — works for any cooling system capacity.
Coolant Mix Calculator
System capacity + target % → litres of each
How It Works
The required volume of antifreeze concentrate is the system capacity multiplied by the target percentage. The remainder is distilled water. Using pre-mixed coolant bypasses this calculation entirely.
How to Use This Calculator
- Check your owner's manual or expansion tank for system capacity.
- Enter the desired antifreeze concentration — 50% is a common all-climate mix.
- If refilling partially, enter the current estimated concentration.
- Click Calculate — amounts of antifreeze and water appear.
- Always use distilled water, never tap water (minerals corrode the system).
Worked Example
Reference Table
| Antifreeze % | Freeze Protection | Boil Protection | Recommended For |
|---|---|---|---|
| 30% | −16°C (3°F) | 103°C (217°F) | Mild climates only |
| 40% | −24°C (−11°F) | 106°C (223°F) | Temperate use |
| 50% | −37°C (−35°F) | 108°C (226°F) | Standard all-climate |
| 60% | −52°C (−62°F) | 111°C (232°F) | Cold climates |
| 70% | −68°C (−90°F) | 114°C (237°F) | Extreme cold only — do not exceed |
Frequently Asked Questions
Can I mix different coolant brands or colours?
Different coolant technologies (OAT, HOAT, IAT) should not be mixed — incompatible additives can form gel. Check the colour (and the actual spec) before topping up. When in doubt, flush and refill with a single type.
Should I use distilled or tap water in the coolant mixture?
Always use distilled or deionised water. Tap water contains minerals (calcium, magnesium) that deposit inside the cooling system as scale, reducing heat transfer and causing corrosion over time.
What concentration is safe in extremely cold climates?
The maximum practical concentration is 70% antifreeze. Above this, freeze protection actually decreases and heat transfer efficiency drops. Never use straight antifreeze — it freezes at around −13°C.
How do I test my current antifreeze concentration?
A refractometer (around $10) is the most accurate method — place a drop on the prism and read the scale. Float-type testers are less accurate but acceptable. Test strips also work and are available at auto parts stores.
