Liquid Mixing Temperature Calculator
Written by Thierno Sadou Diallo, formula verified per our methodology • Last checked on 10/11/2026
The final temperature of a mix of two liquids is calculated with (mass1 × temperature1 + mass2 × temperature2) ÷ (mass1 + mass2), a mass-weighted average. For 200 g at 90°C mixed with 300 g at 10°C, the final temperature is 42°C.
Explanation
When mixing two liquids at different temperatures with no change of state (no melting ice, no boiling), the mixture's final temperature is calculated by conservation of thermal energy: the heat lost by the hotter liquid as it cools is exactly equal to the heat gained by the colder liquid as it warms up. This calculator assumes both liquids have the same specific heat capacity, a reasonable approximation for most water-based liquids found in the kitchen (water, milk, most diluted syrups): under this assumption, the final temperature is simply the average of the two starting temperatures, weighted by their respective masses — the more abundant liquid has more influence on the final result than the minority one, even if the initial temperature gap is large. This formula is useful in many everyday cooking situations: preparing a baby bottle at the right temperature by mixing hot and cold water, quickly cooling a pot of hot liquid by adding a known volume of cold liquid, or anticipating a mixture's temperature before serving it. For a dilution that changes a liquid's concentration rather than its temperature, see our concentrated syrup dilution calculator; for cooling with ice (which additionally involves a change of state, and thus a latent heat absent from this calculation), see our ice to cool a drink calculator.
Example: 200 g at 90°C mixed with 300 g at 10°C
Inputs
Liquid 1: 200 g at 90°C. Liquid 2: 300 g at 10°C.
Calculation
Final temperature = (200 × 90 + 300 × 10) ÷ (200 + 300) = (18000 + 3000) ÷ 500 = 42°C.
Result
This mix of the two liquids reaches a final temperature of 42°C.
Frequently asked questions
Why isn't the final temperature simply the arithmetic average of the two starting temperatures?
Because the final temperature also depends on the respective masses, not just the two temperatures: a small volume of very hot liquid added to a large volume of cold liquid only warms the whole up moderately, while two equal volumes do give exactly the simple arithmetic average of the two temperatures. The formula weights each temperature by its liquid's mass, exactly like a standard weighted-average calculation.
Does this formula work for mixing water and milk?
Approximately yes: milk's specific heat capacity is very close to water's (milk being more than 85% water), which makes this approximation reliable for everyday cooking use like preparing a baby bottle. For liquids very different from water (oil, very concentrated syrup), the approximation becomes less accurate, as these liquids' real heat capacity departs further from water's.
What happens if one of the two liquids contains ice rather than just being cold?
This calculator no longer applies directly in that case: melting ice consumes extra energy (the latent heat of fusion), which this simple weighted average of temperatures doesn't account for. See our ice to cool a drink calculator, which specifically includes this change of state.