Correct a hydrometer reading for temperature
A hydrometer floats at a height set by the liquid’s density, and density changes with temperature. Warm wort, must or juice is thinner than the cool liquid the instrument was calibrated for, so the hydrometer sinks a little further and reads low. This hydrometer temperature correction calculator takes your reading, the temperature of the sample and the calibration temperature printed on the instrument, and gives the corrected specific gravity.
It suits home brewers, winemakers, cider and mead makers and anyone measuring sugar syrups. Once you have the corrected value you can carry it into the ABV calculator to turn the original and final gravities into alcohol by volume. Everything runs in your browser; nothing is uploaded.
How to use the Hydrometer Temperature Correction
- Enter the specific gravity you read from the hydrometer, such as 1.050.
- Enter the temperature of the sample at that moment, in °F or °C.
- Enter the calibration temperature printed on the hydrometer (often 60 °F / 15.6 °C or 68 °F / 20 °C), or pick one from the menu.
- Read the corrected gravity and the correction in points; the table shows the same reading at other temperatures.
Hydrometer Temperature Correction features
Both calibrations
Pick 60 °F (15.6 °C) or 68 °F (20 °C), or type the figure from your own instrument.
°F or °C
Switching units converts the boxes so the numbers keep their meaning.
Shows the working
The two density factors are printed so you can check the arithmetic.
Comparison table
Seven temperatures from cold to warm show how large the error would be.
Plato as well
The corrected value is also given in points and °Plato.
The formula
The correction multiplies your reading by the ratio of two water-density factors: corrected = reading × f(sample temperature) ÷ f(calibration temperature), where f(T) = 1.00130346 − 0.000134722124·T + 0.00000204052596·T² − 0.00000000232820948·T³ and T is in degrees Fahrenheit. It is the polynomial brewers have used for years to describe how water expands as it warms. A reading of 1.050 taken at 77 °F (25 °C) on a hydrometer calibrated at 60 °F (15.6 °C) corrects to about 1.052.
The size of the error is small near the calibration temperature and grows quickly as the sample gets warmer. A few degrees makes less than a point of difference, while a sample at 100 °F can be off by 5 to 6 points, enough to alter your estimate of alcohol by almost 1% on a strong must.
Taking a better reading
- Cool the sample in a jar standing in cold water, and measure again, rather than relying on a big correction.
- Degas it. Bubbles cling to the hydrometer and lift it; stir or pour between two jars first.
- Spin the hydrometer to release bubbles and read at the bottom of the meniscus.
- Use a clean, tall jar wide enough that the instrument floats freely.
- Check the instrument in water at its calibration temperature; it should read 1.000.
Limits and a different instrument
The polynomial describes water and dilute sugar solutions, and it is an approximation at high gravity. Refractometers usually have their own automatic temperature compensation. Spirit hydrometers that read alcohol by volume work from published density tables, so use the correction chart supplied with the instrument rather than this page. Home production of alcohol is regulated differently in each country; check your local rules.
Hydrometer Temperature Correction FAQ
Does hydrometer temperature matter?
Yes. Warm liquid is less dense, so a hydrometer reads lower than the true gravity. At 77 °F (25 °C) the error is about 2 points on a 60 °F-calibrated instrument, and it grows as the sample warms.
What is the hydrometer temperature correction formula?
Corrected SG = reading × f(sample °F) ÷ f(calibration °F), with f(T) = 1.00130346 − 0.000134722124·T + 0.00000204052596·T² − 0.00000000232820948·T³. The page prints the working with your numbers.
What calibration temperature should I use?
Use the one printed on your hydrometer. Many brewing hydrometers use 60 °F (15.6 °C) and many wine hydrometers 68 °F (20 °C). If it is not marked, 68 °F is a common default, but check the box or instructions.
Do I add or subtract the correction?
For a sample warmer than the calibration temperature, add; for a cooler one, subtract. The calculator states the sign and gives the final value.
Can I use this for an alcohol hydrometer?
No. A spirit hydrometer reads percent alcohol by volume and its temperature table is different. Use the table supplied with the instrument.
Is the correction needed for a refractometer?
Most refractometers compensate for temperature automatically, within a stated range. After fermentation starts they need a separate alcohol correction, which the ABV calculator provides.