Coolant Mix Calculator
How much antifreeze to add for the protection you need.
Enter your values
Enter the cooling system capacity in L.
Enter the target antifreeze concentration in %.
Enter the current concentration in the system in %.
Results update instantly as you type — no submit needed. Your values are remembered on this device, and the shareable link reopens the calculator with exactly these numbers.
- Concentrate to add
- 4 L
- Water to add
- 4 L
- Freeze protection
- -37 °C (-34 °F)
- Boil protection (15 psi cap)
- ≈129 °C / 265 °F
- Mix ratio
- 50% coolant : 50% water
Quick answer
A 50/50 glycol mix protects to about −37 °C and raises the boiling point to about 129 °C under a 15 psi cap; going above 70% concentrate actually cools worse.
Concentrate = system capacity × target %
At a glance
| What it does | How much antifreeze to add for the protection you need. |
|---|---|
| Category | Auto |
| Inputs needed | Cooling system capacity, Target antifreeze concentration, Current concentration in the system |
| Main output | Concentrate to add |
| Formula | Concentrate = system capacity × target % |
| Cost | Free — no sign-up, no download |
How to use the Coolant Mix Calculator
- 1Find the total cooling system capacity in your handbook.
- 2Choose the target concentration — 50% suits most climates, 60% for hard winters.
- 3Enter the current concentration if you are topping up rather than refilling.
Inputs explained
- Cooling system capacity(L)
- Enter the cooling system capacity in L.
- Target antifreeze concentration(%)
- Enter the target antifreeze concentration in %.
- Current concentration in the system(%)
- Enter the current concentration in the system in %.
Worked example
Using the values the calculator loads with:
Inputs
- Cooling system capacity8 L
- Target antifreeze concentration50 %
- Current concentration in the system0 %
Results
- Concentrate to add4 L
- Water to add4 L
- Freeze protection-37 °C (-34 °F)
- Boil protection (15 psi cap)≈129 °C / 265 °F
- Mix ratio50% coolant : 50% water
Frequently asked questions
Can I use pure antifreeze?
No. Neat glycol transfers heat far worse than a mix and actually freezes at a higher temperature than a 60/40 blend.
Which water should I use?
Deionised or distilled water only. Tap water leaves scale and minerals that corrode the radiator and heater core.
What do I need to enter into the Coolant Mix Calculator?
Just 3 values: cooling system capacity, target antifreeze concentration, current concentration in the system. Every field starts with a realistic example, so you can change one number at a time and watch the result update instantly.
How does the Coolant Mix Calculator work out the answer?
A 50/50 glycol mix protects to about −37 °C and raises the boiling point to about 129 °C under a 15 psi cap; going above 70% concentrate actually cools worse. It applies the formula Concentrate = system capacity × target % and shows the working so you can check each step by hand.
Is the Coolant Mix Calculator free, and do I need an account?
It is completely free with no sign-up, no download and no usage limit. Everything is calculated in your browser, so the numbers you type never leave your device.
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.