Hydrometer temperature correction calculator

A hydrometer reads true only at the temperature it was calibrated at. Enter the reading and the sample’s temperature for the corrected gravity.

How it works

A liquid gets less dense as it warms, so a warm sample reads low and a cool one reads high. The correction scales the reading by the density of water at the two temperatures:

corrected = reading × f(sample) ÷ f(calibration)

f is a fit to the density of water, good to within 0.0002 from 0 to 100 °C. The guide has the formula in full and a correction chart.

Worked examples

• 1.050 read at 30 °C on a 20 °C hydrometer is 1.053: 2.6 points higher than it shows.
• 1.050 read at 80 °F on a 60 °F hydrometer is 1.052.

Good to know

• The calibration temperature is printed on the hydrometer, usually 20 °C or 60 °F.
• A sugary wash expands a little more than water, so far from calibration the correction falls short. Cool a sample that is more than 10 °C (18 °F) away.
• This is for a wash or wort. Spirit needs the alcoholmeter calculator, which uses the alcohol tables.