Coolant Mix Ratio Calculator

Inputs

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Total mix volume — the machine sump (or tank) capacity for a fill, the current sump volume for a correction.
gal
Percent of total mix (the shop "8% coolant" convention). General-purpose machining commonly runs 5-10%; the coolant TDS governs.
%
From the coolant data sheet: actual % = Brix reading × factor. Typically 1.0-2.5; 1.0 if you only want the straight Brix relation.

Results

Default result
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Concentrate(V_c)
4gal
Pass

Always add concentrate to water, not water to concentrate, and ideally through a mixer.

In the fresh mix — or to add when raising a lean sump.

Also computed

Water(V_w)46gal

In the fresh mix — or to add when cutting a rich sump.

Water : concentrate at target11.5: 1

Refractometer target5.33Brix

Target % ÷ factor — the reading a correctly mixed sump shows.

Method notes 4 notes
  • Concentration is % of total mix; the equivalent "parts" callout is (100 − c)/c parts water to 1 of concentrate — 8% ≈ 11.5 : 1.
  • Evaporation removes water, not concentrate: sumps drift RICH between top-offs, so top off leaner than the running target (many shops use half-strength).
  • Tramp oil and dissolved tooling soaps inflate Brix readings — skim and mix before trusting the number; the factor itself comes from the coolant data sheet.
  • Charge water quality, biocide schedule and the actual running band per the coolant TDS; this screen does the mixing arithmetic only.

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