Hydrometer Temperature Correction Calculator
A hot or cold sample makes your hydrometer lie. Enter the reading, the temperature of the sample, and the temperature your hydrometer is calibrated to, and get the true specific gravity to use in your ABV and attenuation math.
Most brewing hydrometers are calibrated at 60 °F — check the scale inside yours and enter its value.
Formula & how it works
The corrected gravity is reading × D(sample) ÷ D(calibration), where D is a fourth-order polynomial in temperature (°F) that models the density of water: D(t) = 1.00130346 − 1.34722124e‑4·t + 2.04052596e‑6·t² − 2.32820948e‑9·t³.
Celsius inputs are converted to Fahrenheit first with °F = °C × 9⁄5 + 32.
Worked example
A reading of 1.050 taken at 80 °F on a hydrometer calibrated to 60 °F corrects up to about 1.0033 higher — a true gravity near 1.0533. Left uncorrected, that would understate your ABV by a few tenths of a percent.
Trustworthy gravity readings
Which way the error goes
Warm liquid is less dense, so the hydrometer floats lower and shows a reading below the truth — that is why a hot sample needs an upward correction. A sample colder than calibration is denser, floats the hydrometer higher, and reads high, needing a downward correction. The bigger the gap from the calibration temperature, the bigger the fix.
Know your calibration temperature
The correction hinges on the temperature your hydrometer is actually calibrated to. Sixty degrees Fahrenheit is the most common, but some instruments use 68 °F or 20 °C, and using the wrong value quietly biases every reading. It is printed on the paper scale inside the hydrometer — check it once and note it.
When you can, just cool the sample
Correction math is reliable for moderate gaps, but the most accurate reading of all is one taken near the calibration temperature. If precision matters — final gravity before packaging, say — draw the sample and let it settle close to 60 °F before you read it, then only a small correction is needed.