Hydrometer Temperature Correction
Correct a hydrometer reading taken warmer or cooler than its calibration temperature, from the density of water (Tanaka 2001), in °F or °C.
The corrected specific gravity, how many points the temperature moved it, the corrected °Plato, and both temperatures in °C — for samples between 0 and 40 °C.
Example: 1.048 read at 80 °F on a hydrometer calibrated at 60 °F is really 1.0505, 2.5 points higher; 1.012 at 28 °C on a 20 °C hydrometer is 1.014.
Warm reads
low.
Why temperature changes a reading, how the correction is built from the density of water, and where it stops.
Why it matters
A hydrometer floats deeper in a lighter liquid, and liquids get lighter as they warm. Read above its calibration temperature — printed on the stem or the paper scale, often 60 °F or 20 °C — it reads low; below, it reads high.
The correction
The reading is multiplied by the density of water at the calibration temperature over its density at the sample temperature. The densities come from the CIPM formula of Tanaka et al. (Metrologia, 2001), valid from 0 to 40 °C.
Assumptions
Wort and beer are taken to expand with temperature as water does, which is close for ordinary gravities, and the glass’s own expansion is ignored. Both effects are small next to a reading taken 20 degrees off.
What the correction does not settle
Hot wort is outside the formula’s range and also risky to handle: cool the sample below 40 °C (104 °F) before reading. A sample far from calibration is better cooled than corrected. Inputs stay in your browser; the same anonymous usage counts as the rest of the site apply.
SOURCES
- Tanaka et al., Recommended table for the density of water between 0 °C and 40 °C, Metrologia 38 (2001) 301–309
- ASBC Methods of Analysis — extract (°Plato) table, as its cubic fit in specific gravity
Last reviewed 24 September 2026. How results are checked: How we verify.