Antifreeze Mix Ratio Calculator
Calculate the correct antifreeze to water ratio for your climate.
Find freeze and boil-over protection for any coolant concentration.
Antifreeze (also called engine coolant) is a mixture of ethylene glycol (or propylene glycol) and water. It does two jobs: it lowers the freezing point of the coolant below the coldest temperatures in your climate, and it raises the boiling point above 100°C (212°F) to prevent overheating.
Why Not Use Pure Antifreeze?
Counterintuitively, pure (100%) antifreeze actually freezes at about −13°C (8°F) — much warmer than a 50/50 mix, which freezes at about −37°C (−34°F). Water is needed to improve heat transfer and to achieve the best freeze protection. The optimal mix is typically 50–70% antifreeze.
Freeze and Boil-Over Protection by Concentration
| Antifreeze % | Water % | Freeze Point | Boil-Over Point |
|---|---|---|---|
| 30% | 70% | −16°C / 3°F | 108°C / 226°F |
| 40% | 60% | −24°C / −12°F | 110°C / 230°F |
| 50% | 50% | −37°C / −34°F | 112°C / 234°F |
| 60% | 40% | −52°C / −62°F | 116°C / 241°F |
| 70% | 30% | −55°C / −67°F | 120°C / 248°F |
| 100% | 0% | −13°C / 8°F | 197°C / 387°F (pure) |
Always Use Distilled Water
Tap water contains minerals that can deposit on engine surfaces and corrode aluminum components. Always use distilled water when mixing coolant. Pre-mixed coolant already uses distilled water.
Coolant System Capacity
Before mixing, know your vehicle’s coolant system capacity (found in the owner’s manual). Typical capacities:
- Small car: 6–8 litres (1.5–2 gallons)
- Sedan/SUV: 8–12 litres (2–3 gallons)
- Truck: 12–18 litres (3–4.5 gallons)
Types of Antifreeze
| Type | Color | Change Interval |
|---|---|---|
| IAT (Inorganic) | Green | Every 2 years / 30,000 miles |
| OAT (Organic) | Orange, red, or pink | Every 5 years / 150,000 miles |
| HOAT (Hybrid) | Yellow or turquoise | Every 5 years / 150,000 miles |
Never mix different types. When in doubt, flush the system completely and refill with the correct type.
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