Coolant Mix Calculator
Find antifreeze and water for a coolant mix.
50% protects to ~ −37°C
Results update as you type.
How it works
Engine coolant is a mix of antifreeze (usually ethylene or propylene glycol) and water, and this calculator finds how much of each to combine for your target concentration. You enter the total volume of coolant you need and the desired antifreeze percentage, and it returns the volumes of antifreeze and water to mix. The standard mix is 50/50, which protects most engines from freezing down to roughly −37°C (−34°F) and raises the boiling point, while also carrying corrosion inhibitors that protect the cooling system. In very cold climates you might go up to about 60 or 70 percent antifreeze for lower freeze protection, but going beyond about 70 percent actually reduces performance, since pure antifreeze has a higher freezing point than a mix and transfers heat less well than water. Water is essential for heat transfer, so a balanced mix is important. Use distilled or deionized water rather than tap water to avoid mineral deposits and corrosion. Note that some products are sold pre-mixed at 50/50 and should not be diluted further, while concentrate must be mixed with water — check the label. This calculator makes it easy to prepare the right amount for a coolant flush or top-up. Enter the total volume and target percentage to find the amounts.
Antifreeze = total × (antifreeze % ÷ 100); water = total − antifreeze
For a target concentration, the antifreeze volume is the total coolant volume times the target percentage divided by 100, and the water is the remaining volume. A 50/50 mix is standard, protecting against both freezing and boiling while providing corrosion protection.
Source:Coolant mixing ratios
We review all our tools from time to time to ensure accuracy.
Worked example
How to use this calculator
- 1
Enter your values
Enter total coolant volume.
- 2
Adjust the options
Adjust target antifreeze percentage if they apply — sensible defaults are already set.
- 3
Read your result
Antifreeze needed updates instantly as you type — no button to press.
Frequently asked questions
What is the right coolant mix ratio?
A 50/50 mix of antifreeze and water is standard for most vehicles and climates, protecting against freezing to about −37°C and raising the boiling point while inhibiting corrosion. Colder climates may use up to 60 or 70 percent antifreeze, but higher concentrations are not recommended because they cool less effectively and can actually freeze at a higher temperature.
Why not use pure antifreeze?
Pure antifreeze is a worse coolant than a mix. It transfers heat less effectively than water and, surprisingly, has a higher freezing point than a diluted mix — a 100 percent solution can freeze around −20°C, warmer than a 50/50 blend. Water is needed for heat transfer, so always mix antifreeze with water rather than running it straight.
What water should I use for coolant?
Use distilled or deionized water, not tap water. Tap water contains minerals and impurities that can form scale deposits, cause corrosion, and reduce the cooling system's efficiency over time. Distilled water is inexpensive and keeps the system clean, so it is the recommended choice whenever you mix concentrate with water for coolant.
Is pre-mixed coolant already diluted?
Yes. Pre-mixed or ready-to-use coolant is already blended to a 50/50 ratio and should be poured in as-is, not diluted further, or you will weaken the protection. Concentrated antifreeze, by contrast, must be mixed with water before use. Always check the product label to know whether you have concentrate or a pre-diluted mix.
How much antifreeze do I need for a flush?
It depends on your cooling system's total capacity, listed in the owner's manual, typically a few liters for a car. For a full flush at 50/50, you need half that capacity in antifreeze and half in water. Enter your system's capacity as the total volume here to get the exact amounts of each to buy and mix.