About the Hydrometer Temperature Correction
This hydrometer temperature correction calculator adjusts a specific gravity reading for the temperature of the sample. Hydrometers are calibrated to read correctly at one temperature — usually 60°F (15.6°C), sometimes 68°F (20°C) — and liquids expand as they warm, so a hot wort sample reads lower than its true gravity and a cold one reads slightly higher.
Homebrewers, winemakers, cider and mead makers and kombucha brewers use it whenever they cannot wait for a sample to cool: enter the reading, the sample temperature and your hydrometer’s calibration temperature (printed on the paper scale or in the instructions), and you get the corrected gravity, the size of the correction in gravity points and the equivalent degrees Plato.
The correction is based on how the density of water changes with temperature, which is a good approximation for beer and wine strength solutions. It is most accurate within about 20–30°F of the calibration temperature; for very hot samples, cool them to room temperature first for a more reliable reading — and never put a glass hydrometer into near-boiling wort.
With the default inputs, the corrected specific gravity is 1.0524. Change any value above to recalculate instantly.
How to use the hydrometer temperature correction
- 1Take the hydrometer reading at eye level from the bottom of the meniscus.
- 2Measure the sample temperature with a thermometer.
- 3Enter the calibration temperature printed on your hydrometer.
- 4Read the corrected gravity and use it for ABV and efficiency calculations.
Formula and method
A hydrometer floats deeper in a liquid that is less dense. Warming a sample lowers its density, so the instrument reads low; the correction scales the reading by the ratio of water’s relative density at the sample temperature T to that at the calibration temperature C. The cubic ρ(x) is a fit to water-density tables in °F and is the standard formula used in homebrewing calculators.
Celsius inputs are converted to Fahrenheit first. Degrees Plato are calculated from the corrected gravity with the ASBC polynomial °P = −616.868 + 1111.14·SG − 630.272·SG² + 135.997·SG³. Corrections are small near the calibration temperature (about +2.5 points at 80°F for a 60°F hydrometer) and grow quickly for hot samples.
- SG_read
- Gravity shown on the hydrometer
- T
- Sample temperature (°F)
- C
- Calibration temperature (°F)
Worked examples
Warm wort sample at 80°F
Water is about 0.23% less dense at 80°F than at 60°F, so a 1.050 reading taken at 80°F corrects up by roughly 2.5 points to 1.0525 (1.052 rounded).
Hot sample at 120°F, 68°F hydrometer
At 120°F water is about 1% less dense than at 68°F, so a 1.040 reading corrects up by roughly 10 points to about 1.050 — a big difference when calculating brewhouse efficiency.
Cool cider sample in Celsius
A 10°C sample is colder (denser) than the 20°C calibration point, so the reading is slightly high: 1.002 corrects down by about 1.5 points to about 1.0005.
Frequently asked questions
Why do hydrometer readings need temperature correction?+
Liquids expand when warm and contract when cold, changing density. A hydrometer calibrated at 60°F reads low in warmer samples and high in colder ones, so the reading must be adjusted to reflect the true gravity.
What temperature is my hydrometer calibrated to?+
Most homebrew hydrometers are calibrated at 60°F (15.6°C); many newer and European ones use 68°F (20°C). The calibration temperature is usually printed on the scale paper inside the stem.
How much does temperature change a gravity reading?+
Relative to a 60°F hydrometer, about +1 point at 70°F, +2.5 at 80°F, +4 at 90°F, +6 at 100°F and around +11 at 120°F. Corrections below the calibration temperature are small and negative.
Can I measure gravity of hot wort?+
You can, but accuracy falls as the temperature rises, and hot liquid can crack glass hydrometers. It is better to cool a small sample in a sealed container or ice bath to near room temperature before reading.
Does this apply to refractometers?+
No. Most refractometers have automatic temperature compensation and read in Brix. Refractometer readings need a different conversion, especially after fermentation when alcohol is present.