Coolant Mix Ratio Calculator

Q: Why is there no chart page?

Mix math is capacity × ratio with interpolated freeze/boil checks. The widget, guide, and a refractometer already give you what a static chart would.

Q: Can I use tap water?

Distilled water for mixing concentrate. Tap water adds minerals that accelerate corrosion and can skew refractometer readings.

Q: Pre-mixed 50/50 or concentrate?

See pre-mixed vs concentrate . Bottled 50/50 is exact but costlier per gallon; concentrate lets you tune for colder climates.

Q: Where are recommended product links?

Affiliate product cards for refractometers and coolant are pending sourcing in the live CSV. Use the calculator and guide now; product picks will appear when sourced.

Quarts and liters of antifreeze concentrate and distilled water for a target mix or freeze point — ethylene glycol / water at 15 psi, fresh fill or top-off

Enter total cooling-system capacity, pick a target mix ratio or freeze-protection temperature, and choose fresh fill vs partial adjust. Get concentrate and water volumes, freeze/boil points, and top-off drain math. Method: coolant mix guide. Field failures: troubleshooting. Pre-mixed vs concentrate: comparison. Related: MPG, trip fuel cost, towing capacity. Hub: automotive tools.

Starting point, not a fill sheet — verify against the owner’s manual and measure with a refractometer. Ethylene-glycol/water curves vary by additive package (OAT/HOAT/IAT). This tool uses published EG/water freeze and boil points at 15 psi radiator cap pressure. Never exceed ~70% concentrate — freeze protection stops improving and boil protection can fall after the eutectic. Distilled water only for mixing concentrate; tap water adds minerals that accelerate corrosion. Do not mix incompatible coolant chemistries in the same system.

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How to Use This Coolant Mix Calculator

Look up total cooling-system capacity in the owner’s manual. Choose quarts or liters. Pick a target 50/50-style ratio or enter a freeze-protection goal for your climate. For a partial refill, switch to top-off mode and enter the current refractometer reading. Calculate. Verify with a refractometer before you close the cap.

Fresh fill: concentrate = capacity × r, water = capacity × (1 − r)
Adjust up (r > c): drain & replace concentrate = capacity × (r − c) / (1 − c)
Adjust down (r < c): drain & replace water = capacity × (c − r) / c
r = target concentrate fraction; c = current concentrate fraction

Worked example — 12 qt system, 50/50 fresh fill Capacity 12 qt at 50% concentrate → 6.00 qt concentrate + 6.00 qt distilled water. Interpolated freeze protection −34°F (−37°C), boil at 15 psi 265°F (129°C).

Why the curve behaves this way: guide. Overheating from bad mix: troubleshooting.

What This Number Is (and Is Not)

The volumes are straight algebra on system capacity and target concentration. Freeze and boil outputs interpolate published ethylene-glycol/water points at 15 psi cap pressure. They are planning numbers for EG-based coolant mixed with distilled water.

They are not a substitute for the coolant label on the bottle, the vehicle owner’s manual, or a refractometer reading on the fluid already in the block. Propylene-glycol coolants, factory pre-mixed OAT/HOAT packages, and altitude/cap-pressure changes shift real freeze/boil behavior. Never mix IAT, OAT, and HOAT chemistries hoping the math will save you.

Never exceed ~70% concentrate. Freeze protection stops improving past the eutectic and boil protection can fall. More antifreeze is not always more protection.

Coolant Mix FAQ

Why is there no chart page?

Mix math is capacity × ratio with interpolated freeze/boil checks. The widget, guide, and a refractometer already give you what a static chart would.

Can I use tap water?

Distilled water for mixing concentrate. Tap water adds minerals that accelerate corrosion and can skew refractometer readings.

Pre-mixed 50/50 or concentrate?

See pre-mixed vs concentrate. Bottled 50/50 is exact but costlier per gallon; concentrate lets you tune for colder climates.

Where are recommended product links?

Affiliate product cards for refractometers and coolant are pending sourcing in the live CSV. Use the calculator and guide now; product picks will appear when sourced.

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