Hydrometer Temperature Correction Calculator

How it works

SG corrected = SG reading × f(T sample) ÷ f(T calibration), where f(T°F) = 1.00130346 − 1.34722124×10⁻⁴·T + 2.04052596×10⁻⁶·T² − 2.32820948×10⁻⁹·T³

A hydrometer measures density, and liquids expand as they warm, so a sample read hot appears less dense — lower gravity — than it really is. Hydrometers are calibrated at a single temperature, usually 60 °F (15.6 °C) or 20 °C, and a wort sample at 30 °C reads about two points low, at 50 °C about eight points low. The correction uses the density-versus-temperature curve of water, which is close enough for wort and wine. It matters most for original gravity, which is often measured warm out of the kettle and sets the ABV calculation. Cooling a small sample in the fridge for ten minutes is more accurate than any correction above about 40 °C.

Worked example

A kettle sample reading 1.046 at 32 °C with a 60 °F hydrometer corrects to 1.050 — about three and a half points higher than it looked.

Frequently asked questions