Hydrometer Correction
Because your sample is never the right temperature
Hydrometers are calibrated at a specific temperature (usually 15°C or 20°C). If your wort sample is warmer or cooler than that, the reading will be off. This calculator corrects for the difference. Enter your reading, sample temp, and calibration temp, and it gives you the true gravity.
Hydrometer Correction
temperature adjustCorrect your hydrometer reading for the sample temperature. Warm wort reads lower than the true gravity — this fixes that.
How We Calculate It
We use the Kell (1975) water density equation, a polynomial that models how water density changes with temperature. The correction compares the density of water at your sample temperature to the density at calibration temperature, then adjusts your gravity reading accordingly.
When does it matter?
At 30°C (86°F), a reading of 1.050 is actually closer to 1.052. At 40°C it's off by about 4 points. For OG readings taken right after chilling, the error is usually small. But if you're reading hot wort or very cold fermented beer, the correction matters for accurate ABV calculations.
Sources
- Kell, G.S. “Density, Thermal Expansivity, and Compressibility of Liquid Water.” J. Chem. Eng. Data 20(1), 1975.
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