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Coolant Mix Ratio Calculator

Work out coolant mix ratio instantly with clear inputs, formula shown and shareable results.

About Coolant Mix Ratio Calculator

To raise concentration you must drain the same volume you add, since the system is already full. Glycol at 50% gives about -37 degrees of freeze protection and raises the boiling point, while going much above 60% actually worsens heat transfer.

Formula

Coolant mix

glycol deficit = capacity x (target - current); drain and replace that volume with concentrate

Worked example

With the default values below, Coolant Mix Ratio Calculator returns Concentrate to add of 1.50. Change any input above and every figure here is recalculated in your browser.

Inputs used

Cooling system capacity
7.5 L
Target glycol concentration
50 %
Current concentration
30 %
Concentrate strength
100 %

Results

Concentrate to add
1.50 L
Coolant to drain first
1.50 L
Freeze protection
-27.50 °C
Boiling point at 1 bar cap
134.00 °C

Step by step

  1. 1Values used
  2. 2Coolant mix
  3. 3Concentrate to add= 1.50 L
  4. 4Coolant to drain first= 1.50 L
  5. 5Freeze protection= -27.50 °C
  6. 6Boiling point at 1 bar cap= 134.00 °C

Assumptions and limits

  • The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Why not use 100% glycol?

Pure glycol has poor specific heat and higher viscosity, so it cools worse than a 50/50 mix and freezes at a higher temperature than 60% glycol.

What concentration gives the best freeze protection?

Around 60-70% glycol reaches about -55 degrees. Beyond that the freeze point rises again, which is why pure antifreeze freezes at only -13.

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Coolant Mix Ratio Calculator – Calculate Concentrate to add