Brewing and winemaking
Hydrometer temperature correction.
Enter your reading, the sample temperature and the hydrometer calibration temperature to get the corrected gravity.
Inputs
Corrected gravity
Enter your numbers.
How it works
A hydrometer floats according to the density of the liquid, and density changes with temperature, so a reading is only exact at the temperature the instrument was calibrated for. Homebrew Academy gives the correction as CG = MG × (P(TR) ÷ P(TC)), where MG is the measured gravity, TR the temperature at the reading, TC the calibration temperature, and P(T) = 1.00130346 − 0.000134722124 T + 0.00000204052596 T² − 0.00000000232820948 T³ with T in degrees Fahrenheit. The Homebrew Academy page prints this formula without its exponents; the tool uses the cubic polynomial, which returns exactly 1 times the reading when the sample is at the calibration temperature. Homebrew Academy notes that older hydrometers are generally calibrated at 59 F and newer ones mostly at 68 F.
Worked example. A reading of 1.050 at 77 F on a hydrometer calibrated at 68 F corrects to 1.0512, an increase of 1.2 points. The same sample as 25 C on a 20 C hydrometer gives the identical result. A warm sample reads low, so the correction is added.
Let the sample cool where you can, and do not use the tool for temperatures outside 32 to 159 F, the range Brewer’s Friend supports. Use the corrected gravity in the ABV, potential alcohol and sugar-addition tools.
Frequently asked questions
Do I need to correct my hydrometer reading for temperature?
Hydrometers are calibrated at one temperature, commonly 59 F or 68 F, so a warmer or cooler sample reads off. Correcting gives the gravity you would see at the calibration temperature.
What is my hydrometer calibration temperature?
It is usually printed on the hydrometer or its packaging. Homebrew Academy says older ones are generally 59 F and newer ones mostly 68 F.
How much does 77 F change a reading?
For a hydrometer calibrated at 68 F, a 1.050 reading at 77 F corrects to 1.0512, about 1.2 points higher.
Does the correction work in Celsius?
Yes. The tool converts to Fahrenheit internally, so 25 C on a 20 C hydrometer gives the same result as 77 F on a 68 F hydrometer.
Sources
Opened
- Homebrew Academy: Hydrometer Temperature Correction Calculator: Gives the correction formula with the 1.00130346 polynomial and notes 59 F and 68 F calibrations.
- Brewer's Friend: Hydrometer Temperature Adjustment Calculator: Supports hydrometer calibrations of 59 F (15 C) and 68 F (20 C) and a temperature range of 32 to 159 F, 0 to 71 C.
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Scope
Estimate from a published polynomial; liquids with high sugar or alcohol may differ slightly. Not a substitute for letting a sample reach the calibration temperature. Not professional advice.