Hydrometer Temperature Correction Calculator
Hydrometers are calibrated at one temperature, usually 60 °F or 68 °F. Enter your reading, the sample temperature, and the calibration temperature to get the corrected specific gravity.
How the correction works
Water’s density changes with temperature in a well-measured way. The calculator estimates the density of water at the sample temperature and at the calibration temperature with a cubic fit, then scales your reading by the ratio of the two. A warm sample is less dense, so its reading is scaled up:
corrected SG = reading × density(calibration temp) ÷ density(sample temp)
This is the formula most homebrew calculators use. It treats the sample like water, which is close enough for beer, cider, and most meads and wines.
Correction table
Corrected values for a reading of 1.050 on a hydrometer calibrated at 60 °F (15.6 °C).
| Sample temperature | Reads | Corrected |
|---|---|---|
| 50 °F (10 °C) | 1.050 | 1.049 |
| 60 °F (16 °C) | 1.050 | 1.050 |
| 70 °F (21 °C) | 1.050 | 1.051 |
| 80 °F (27 °C) | 1.050 | 1.052 |
| 90 °F (32 °C) | 1.050 | 1.054 |
| 100 °F (38 °C) | 1.050 | 1.056 |
Tips for accurate readings
- Cool the sample close to the calibration temperature instead of relying on a large correction.
- Measure the temperature of the sample itself, not the fermenter or the room.
- Spin the hydrometer to knock off bubbles, and degas fermenting samples.
- Read at the bottom of the meniscus, at eye level.
More on taking readings in Specific gravity for homebrewing. Once you have corrected OG and FG readings, use the ABV calculator.
Limitations
- The correction assumes the sample expands like water; very sugary or alcoholic samples differ slightly.
- Corrections more than about 20 °F (10 °C) from the calibration temperature are less reliable.
- Refractometers with automatic temperature compensation don’t need this correction.
References
- American Homebrewers Association — How to take an accurate hydrometer reading
- John Palmer — How to Brew
Frequently asked questions
Why does temperature affect a hydrometer reading?
Liquids expand as they warm, so a warm sample is less dense and the hydrometer sinks further and reads low. A cold sample reads slightly high. The correction adjusts the reading to what it would be at the calibration temperature.
What temperature is my hydrometer calibrated at?
Check the paper scale inside the hydrometer or its instructions. Most homebrew hydrometers are calibrated at 60 °F (15.6 °C); many newer ones use 68 °F (20 °C).
Can I take a gravity reading of hot wort?
You can correct it, but the further the sample is from the calibration temperature, the less reliable the correction. Hot samples also evaporate and can damage a glass hydrometer. Cool the sample to within about 20 °F (10 °C) of the calibration temperature when you can.