Coolant Capacity Mix Calculator
Split your cooling system’s total capacity into concentrated antifreeze and water for a target coolant concentration — the classic 50/50 or a custom ratio.
How it works
Antifreeze = capacity × concentration% · Water = capacity − antifreeze
Concentrated antifreeze must be diluted, and the target concentration decides the split of your total system capacity between concentrate and water. A 50/50 mix is the everyday standard, protecting to roughly −37 °C while still carrying heat away well; colder climates push the antifreeze share up toward 60–70%, beyond which freeze protection actually worsens. Always use distilled water — tap-water minerals scale and corrode the system.
Worked example
A 6-litre cooling system at a 50% target takes 6 × 0.50 = 3 L of concentrated antifreeze and 6 − 3 = 3 L of distilled water — the familiar 50/50 blend.
Frequently asked questions
What is the best coolant-to-water ratio?
A 50/50 mix suits most climates and is what carmakers specify as standard. In severe cold you can go up to about 60–70% antifreeze, but never higher — beyond roughly 70% the freeze protection reverses and heat transfer drops.
Can I use pre-mixed coolant instead?
Yes. Pre-diluted "ready to use" coolant is already 50/50, so you would pour in the full system capacity with no water added. This calculator is for concentrate you mix yourself.
Why distilled water and not tap water?
Tap water carries minerals that form scale and promote corrosion inside the radiator and passages. Distilled or deionised water keeps the system clean and lets the corrosion inhibitors in the antifreeze do their job.
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This calculator is for educational purposes. Double-check important results before acting on them.