Hydrometer Temp. Adj.

BrewCo Brew Tools

Hydrometers are calibrated to give accurate readings at a specific temperature (usually 20°C). If your sample is warmer or colder, this calculator corrects the reading to what it would be at calibration temperature.

How to use it

  1. Take your hydrometer reading as normal.
  2. Note the temperature of the liquid at the time of reading.
  3. Check your hydrometer's calibration temperature (usually printed on the stem — 20°C is standard).
  4. Enter all three values for the corrected reading.
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Why does temperature affect hydrometer readings?

Liquid expands as it warms, becoming less dense — a warm sample will give a lower gravity reading than the true value, and a cold sample will read higher. The difference is small at room temperature but grows significantly above 25°C or below 10°C, so it's always worth correcting if your sample isn't at the hydrometer's calibration temperature.

More free home brew calculators

Buy a Young's Hydrometer at BrewCo UK — essential kit for any home brewer.

How hydrometer temperature correction works

What it does: a hydrometer is only accurate at the temperature it was calibrated at. Most modern hydrometers are calibrated at 20°C, but some older or imported ones are calibrated at 15.6°C (60°F). The temperature is usually printed on the paper scale inside the stem, so check yours and enter it in the third box.

How to use it: take your reading in a trial jar, measure the temperature of the sample, then enter the reading, the sample temperature and your calibration temperature. The corrected gravity appears straight away.

The formula in plain words: warm liquid is less dense, so it reads low; cold liquid reads high. The calculator uses the standard density curve for water to work out how much your sample has expanded or shrunk compared with the calibration temperature, and scales your reading by that amount.

Worked example: you read 1.050 on a sample at 30°C with a 20°C hydrometer. The corrected gravity is about 1.0526. At 25°C the same reading corrects to about 1.0512, and at 10°C it corrects down to about 1.0485. A small change, but enough to shift your ABV and to tell you whether fermentation has really finished.

Once you have corrected OG and FG readings, put them into our ABV calculator.

Frequently Asked Questions
What temperature is my hydrometer calibrated at?
Most hydrometers are calibrated at 20°C, but some are calibrated at 15.6°C (60°F). Check the paper scale inside the stem or the instructions that came with it, and enter that figure in the calculator.
Is it better to correct the reading or cool the sample?
Cooling the sample to the calibration temperature is the most accurate option. If that isn't practical, a corrected reading is fine for home brewing, especially within about 10°C of the calibration temperature.
Does temperature correction change my ABV?
Yes, slightly. If both your original and final readings were taken warm, both read low. Correcting them gives a more accurate ABV, because ABV is worked out as (OG minus FG) multiplied by 131.25.