Free Public health / Plumbing calculator

Hot and cold-water mixing calculator

Calculate mixed-water temperature from two amounts or find hot/cold proportions for a target temperature.

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All values remain in your browser. Review the assumptions before using the result.

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How the calculation works

Simple sensible-heat balance assuming equal fluid properties and no losses.

Formula

Tm = (mhTh + mcTc) ÷ (mh + mc)

Worked example

Hot / cold temperatures60°C / 10°C

Amounts10 L / 10 L

Expected mixed temperature35°C

Assumptions and limitations

Assumptions

Hot and cold streams have equal density and specific heat.
No heat is lost during mixing.

What this does not check

Does not select or verify thermostatic mixing valves.
Does not assess storage hygiene, scald protection, pipe heat loss or draw-off conditions.

Formula version: 1.0 · Last reviewed: 16 August 2026

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Engineering basis: first-principles calculation using user-entered project data. The calculator does not choose design criteria or replace the complete project-specific engineering design.

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