Coolant Concentration Calculator

Refractometers measure how much light bends passing through the coolant sample (Brix scale), not concentration directly. Different coolant formulations refract light differently at the same true concentration, so the manufacturer publishes a correction factor specific to that product. Multiplying the raw reading by that factor is what converts it into an accurate percent concentration -- skipping this step can give a reading that's off by a meaningful margin.

Yes -- for the same percentage-point correction, a larger sump volume requires proportionally more water added, because the dilution formula (C1 x V1 = C2 x V2) scales the water-to-add amount directly with the existing fluid volume. A 500-gallon sump needing a 2% reduction requires far more added water than a 20-gallon sump needing the identical 2% reduction.

A mix ratio of 1:20 means 1 part coolant concentrate is diluted into a total of 20 parts finished fluid (so roughly 19 parts water plus 1 part concentrate). This calculator derives it from percent concentration as 100 divided by the concentration percentage, and reports it for both your current actual mix and your target mix so you can compare them at a glance.

When actual and target concentration are equal, the difference from target is zero, and the calculator recommends adding neither water nor concentrate -- both the "water to add" and "concentrate to add" outputs return zero. The sump is already at the desired concentration and needs no correction.

The "water to add" figure is simply how much water the C1 x V1 = C2 x V2 dilution math requires to hit your target concentration -- it will always increase the total fluid volume, and on a badly over-concentrated sump that amount can approach or exceed the sump's physical capacity. When that happens, don't just pour the full amount in on top of what's already there: drain off roughly that much over-concentrated fluid first, then top the sump back up with fresh water (or pre-mixed fluid at the target concentration) to reach the same result without overflowing.