Thermal Mixing Temperature Calculator
Estimate a blend temperature from hot and cold water volumes. The tool shows the method and key assumptions so you can inspect how the input values lead to the estimate.
How to use this calculator
- Enter hot water volume (litres) using the unit and definition shown beside the input.
- Enter hot water temperature (°c) using the unit and definition shown beside the input.
- Enter cold water volume (litres) using the unit and definition shown beside the input.
- Check that all values refer to the same time period and scenario.
- Review the outputs alongside the assumptions before using them in a decision.
Formula and assumptions
For water with equal specific heat and density, Tmix=(Vhot×Thot+Vcold×Tcold)/(Vhot+Vcold).
- Assumes water only, equal density and heat capacity, and no heat transfer to the vessel or surroundings. Real mixing can differ if volumes, phase or substances differ.
- The estimate is calculated from values you enter. It does not connect to external accounts, obtain live prices, or validate local regulations or engineering specifications.
Worked examples
Worked example
3 L at 70°C mixed with 7 L at 15°C gives an ideal final temperature of 31.5°C.
Use the same volume unit for both portions and temperatures in °C.
Check the actual temperature before using water for any safety-sensitive purpose.
Understanding the result
Assumes water only, equal density and heat capacity, and no heat transfer to the vessel or surroundings. Real mixing can differ if volumes, phase or substances differ.
Change one input at a time to see how sensitive the output is to that assumption.
Important notes
Assumes water only, equal density and heat capacity, and no heat transfer to the vessel or surroundings. Real mixing can differ if volumes, phase or substances differ.
Frequently asked questions
What formula does the Thermal Mixing Temperature Calculator use?
For water with equal specific heat and density, Tmix=(Vhot×Thot+Vcold×Tcold)/(Vhot+Vcold).
What should I verify before relying on the result?
Assumes water only, equal density and heat capacity, and no heat transfer to the vessel or surroundings. Real mixing can differ if volumes, phase or substances differ.
Can I compare different scenarios?
Yes. Change one assumption at a time, keep units and definitions consistent, and save the inputs used for each comparison.
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This page provides a calculation tool plus explanatory information so you can understand what the result means and when the underlying method may not fit your situation.