Coolant & Washer Fluid Mix Ratio Calculator
Split a target volume of coolant or washer fluid into the right amounts of concentrate and water for the concentration you want.
How it works
Concentrate = total × concentration% · Water = total − concentrate · Ratio = concentration% : (100 − concentration%)
Engine coolant and washer concentrate are diluted with water to reach the protection you need. A 50/50 antifreeze mix is the usual all-round choice, giving freeze protection to roughly −37°C and boil protection with the cap on; colder climates may call for up to 60–70% concentrate, but going past about 70% actually reduces freeze protection. Always use distilled or deionized water — tap water minerals can cause scale and corrosion in the cooling system.
Worked example
To make 4 litres of 50% coolant, use 4 × 0.50 = 2 L of concentrate and 2 L of water — a 50:50 mix. For a colder-climate 60% blend of the same 4 L, that is 2.4 L concentrate to 1.6 L water.
Frequently asked questions
What coolant ratio should I use?
A 50/50 concentrate-to-water mix suits most climates and is the standard recommendation. In very cold regions you can raise it toward 60–70% for lower freeze points, but never exceed about 70% — pure or near-pure antifreeze actually freezes at a higher temperature than a proper mix.
Can I use tap water to dilute coolant?
It’s best to use distilled or deionized water. Minerals in tap water can form scale and promote corrosion inside the radiator and engine, shortening the life of the cooling system.
Does this work for windshield washer fluid too?
Yes. Enter the concentrate strength you want and the total volume, and it splits the mix the same way. For winter use, follow the concentrate label to ensure the blend stays liquid at your lowest expected temperature.
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Educational estimate — real figures vary by vehicle, lender, dealer and local rules.