About this tool
The Hydrometer Temperature Correction calculator fixes the error that creeps into a specific-gravity reading when the sample is not at the temperature your hydrometer was calibrated for. Glass hydrometers are usually calibrated at 60 °F (some at 68 °F / 20 °C); water expands as it warms, so a warm sample is less dense and the hydrometer floats lower, reading a gravity that is too low. This free, in-browser tool applies the correction so your logged original and final gravities are accurate. Nothing you enter leaves your device.
The correction uses the standard density-of-water polynomial in degrees Fahrenheit, f(T) = 1.00130346 − 1.34722124×10⁻⁴·T + 2.04052596×10⁻⁶·T² − 2.32820948×10⁻⁹·T³. The corrected reading is SG_corrected = SG_read × f(T_sample) / f(T_calibration). Celsius inputs are converted with F = C × 9/5 + 32 before the polynomial is applied. The result is shown to three decimal places along with the gravity-point delta (points = ΔSG × 1000) that the correction added or removed.
As a worked example, a hydrometer reading 1.050 in an 80 °F sample, calibrated at 60 °F, corrects up to about 1.052 — roughly +2 points — because the warm wort was reading low. The colder the sample below calibration the smaller the correction, and near the calibration temperature the correction is negligible. Always let a hot sample cool toward the calibration temperature when you can; the correction is most reliable within roughly 40–100 °F.