How to use this calculator
- Take the hydrometer reading at the bottom of the meniscus.
- Measure the temperature of the sample in the test jar.
- Choose the calibration temperature printed on your hydrometer.
- Press Calculate and use the corrected gravity in your brewing log or the ABV calculator.
How hydrometer correction works
A hydrometer reads the density of a liquid relative to water at its calibration temperature. When the sample is warmer it is less dense, so the hydrometer sinks further and reads low; a cold sample reads high. The correction multiplies the reading by the ratio of water's relative density at the sample and calibration temperatures, using this widely used cubic approximation (temperatures in °F):
f(t) = 1.00130346 − 0.000134722124·t + 0.00000204052596·t² − 0.00000000232820948·t³
Corrected SG = Measured SG × f(sample) ÷ f(calibration)This models the sample as water. It is the common approach for brewing samples, but it is not suitable for distilled spirits, which need an ethanol-specific correction.
Example
A wort sample reads 1.050 at 80 °F (26.7 °C) on a hydrometer calibrated at 60 °F. The corrected gravity is 1.052.
Accuracy & limitations
- Accepted inputs: gravity 0.990–1.200 and sample temperature 0–60 °C (32–140 °F).
- The approximation assumes the sample expands like water; very sugary samples far from calibration temperature will carry more error.
- For best accuracy, cool or warm the sample to within about 5 °C of the calibration temperature.
FAQ
What calibration temperature is my hydrometer?
It is usually printed on the hydrometer's paper scale or on its box, for example '60°F', '15.6°C', '20°C' or '68°F'. Most brewing hydrometers sold in the US are calibrated at 60 °F; many European ones at 20 °C.
Should I correct readings or just cool the sample?
Cooling the sample close to the calibration temperature is the most accurate approach. The correction is intended for samples within a few tens of degrees of the calibration temperature; the further away, the larger the error.
Is this the same as alcohol temperature correction?
No. This corrects the specific gravity of wort, must or juice. To correct an alcoholmeter reading of a spirit in %vol, use the alcohol temperature correction calculator, which uses a different, ethanol-specific table.
Does this work for refractometers?
No. Most refractometers compensate for temperature automatically (ATC), and their readings need a different correction once alcohol is present.