🌡️ Hydrometer Temperature Correction
Enter your hydrometer reading, the sample temperature and the hydrometer's calibration temperature to get the corrected gravity.
Corrected gravity
1.053
Correction
+0.003
Hydrometers are calibrated at one temperature (commonly 20 °C / 68 °F, or 15.5 °C / 60 °F). A warm sample is less dense, so the hydrometer reads low — this adds the correction back. The effect is small near calibration temperature but grows for hot wort straight off the boil. Check your hydrometer's calibration temperature (printed on the scale) and set it above. 🔒 In your browser.
How the hydrometer temperature correction works
Liquids expand when warm, so a hot sample is less dense and the hydrometer floats lower — reading a gravity that's too low. Hydrometers are calibrated to be exact at one temperature (often 20 °C / 68 °F or 15.5 °C / 60 °F). The tool applies the standard density correction to convert your reading at the sample temperature back to the true gravity.
The correction is tiny near the calibration temperature but grows for a hot sample taken straight off the boil — where it can shift the reading by several points. Check the calibration temperature printed on your hydrometer's scale and enter it, since cheaper hydrometers are often calibrated at 20 °C and some at 15.5 °C. Better still, cool the sample close to calibration temperature before reading.
Frequently asked questions
Do I need to correct hydrometer readings for temperature?
Yes, unless the sample is at the hydrometer's calibration temperature. A warm sample reads low; the correction adds the difference back. It's small near calibration temperature but significant for hot wort.
What temperature are hydrometers calibrated at?
Commonly 20 °C (68 °F), though many are calibrated at 15.5 °C (60 °F). The calibration temperature is printed on the hydrometer's paper scale — enter that value so the correction is right.
How much does temperature change a hydrometer reading?
Near calibration temperature, almost nothing. But a sample at 40 °C read on a 20 °C hydrometer can be off by several gravity points, enough to matter for OG and ABV. The hotter the sample, the bigger the correction.
Should I cool my sample before reading?
Ideally yes — cooling to near the calibration temperature makes the reading accurate without correction. When that's not practical (checking a boiling wort), take the reading and apply the correction here.
Which way does the correction go?
For a sample hotter than calibration temperature, the true gravity is higher than the reading (the correction is positive). For a colder sample it's slightly lower. The tool shows the corrected value and the size of the correction.