Coolant & antifreeze mix calculators
Blend antifreeze and water to the percentage your climate and OEM require. Pick a container and copy the fill amounts.
Engine cooling systems are sensitive to concentration. Too much antifreeze reduces heat transfer; too little sacrifices freeze and boil protection. These presets cover 30/70 through 70/30 blends recommended for modern vehicles and heavy-duty fleets.
Toggle to weight mode if you track coolant by mass. The calculator keeps the fraction the same when you change the total volume, so you can size mixes for any radiator capacity or overflow bottle.
Use the climate table below to match a mix to local lows. Always verify with a refractometer or hydrometer after filling and bleeding the system.
Popular use cases
- Preparing a 5 L fill after a coolant flush
- Mixing a 40/60 gallon for winter-ready protection
- Bottling a 50/50 OAT top-off mix for overflow tanks
- Scaling a 15 L HOAT fleet refill with heavier density defaults
Blend a coolant refill
Kick off with a 50/50 coolant mix sized for a 1 gallon jug. Adjust the percentage, switch to liters, or scale the total for your cooling system.
Defaults: 1 gallon total, 50/50 split.
Coolant blends by climate goal
Hot climates & track days
Lean coolant cuts that maximize heat rejection in warm conditions.
Mild climate maintenance
Balanced fills for temperate regions and shoulder-season service.
Year-round 50/50 protection
OEM-aligned mixes compatible with most modern systems.
Severe-cold prep
High-glycol mixes for sub-zero regions and winter storage.
Maximum corrosion protection
Heavy-duty ratios for diesels and long-haul storage.
Featured calculators
Climate guide
| Climate | Suggested mix | Notes |
|---|---|---|
| Extreme cold (≤ -40°F / -40°C) | 60% coolant / 40% water | Aim for HOAT or high-glycol mixes. Check freeze point with a refractometer before deep winter trips. |
| Four-season regions (-20°F / -29°C lows) | 50% coolant / 50% water | Most OEM guidance. Works with premix bottles and protects against corrosion year-round. |
| Mild climates (above 10°F / -12°C) | 40% coolant / 60% water | Improves heat rejection in hot traffic. Use distilled water and verify corrosion inhibitors annually. |
| Track day or desert use | 30% coolant / 70% water | Maximizes heat shedding. Confirm the mix still meets your minimum freeze protection during storage. |
FAQs
How do I choose the right coolant percentage?
Check your owner’s manual or service information. Many OEMs recommend 50/50 year-round, while milder climates can run 40/60 or even 30/70 to improve heat rejection. Use a refractometer or hydrometer after filling to confirm.
Can I use distilled water instead of deionized?
Distilled water is generally acceptable for mixing with modern OAT/HOAT coolants. Avoid tap water—minerals can precipitate and corrode the system. Some premixes already include deionized water, so double-check your concentrate label.
What if I need a different container size?
Change the total volume in the calculator modal. The ratio stays at your selected percentage, and the parts update instantly for both volume and grams.
What tool should I use to verify the mixture?
A refractometer or floating hydrometer lets you confirm freeze and boil points in seconds. Pull a sample once the thermostat opens, compare the reading to your service chart, and adjust by adding concentrate or water as needed.
Does coolant type affect density?
Yes. OAT coolants often sit near 1.05 g/mL, while HOAT and silicated formulas can reach 1.12 g/mL. The presets preload both to make weight conversions accurate—swap densities if your SDS lists different numbers.