Hydrometer Temperature Correction Calculator
Correct your hydrometer specific gravity readings when your wort or beer sample isn't at the hydrometer's calibration temperature. This calculator uses the standard polynomial correction to give you an accurate OG or FG every time, so your ABV and recipe stats are spot on.
Results
Why does temperature correction matter?
Hydrometers measure the density of a liquid, and liquid density changes with temperature. Hot wort is less dense than cold wort, so a hydrometer reads lower than the true gravity when the sample is hot, and higher when very cold.
A reading taken at 80°F on a 60°F-calibrated hydrometer is off by about 3 gravity points — enough to push your calculated ABV off by 0.4% or mislead you about whether fermentation has finished. Always correct, or wait for your sample to reach calibration temperature.
Most homebrewing hydrometers are calibrated at 60°F (15.6°C). Some lab-grade hydrometers calibrate at 68°F (20°C). Check the printed label on your hydrometer.
Correction at a glance (60°F hydrometer)
| Sample temp (°F) | Sample temp (°C) | Approx. correction |
|---|---|---|
| 50 | 10 | −0.6 points |
| 60 (calibration) | 15.6 | 0.0 points |
| 70 | 21 | +0.9 points |
| 80 | 27 | +2.4 points |
| 90 | 32 | +4.2 points |
| 100 | 38 | +6.5 points |
| 120 | 49 | +12.6 points |
| 150 | 66 | +25.8 points |
How This Calculator Works
A hydrometer is only accurate at one temperature — the calibration temperature etched on its scale. Because liquid density changes with heat, a reading taken at any other temperature needs adjusting. This tool uses the standard fourth-order density polynomial built into most brewing software, which models the density of water across the range brewers actually use.
For a temperature T in °F it computes a density factor D(T) = 1.00130346 − 0.000134722124·T + 0.00000204052596·T² − 0.00000000232820948·T³. The corrected gravity is then your measured reading scaled by the ratio of the two density factors: corrected SG = measured SG × D(sample temp) ÷ D(calibration temp). It also reports the result in degrees Plato using the standard cubic SG-to-Plato conversion.
A Worked Example
Suppose you pull a sample of cooling wort, your hydrometer reads 1.050, the sample is at 80°F, and the hydrometer is calibrated to 60°F.
The density factor at 80°F works out to about 0.99823, and at 60°F to about 0.99907. The corrected gravity is 1.050 × (0.99907 ÷ 0.99823) ≈ 1.0529 — roughly +3 gravity points. That seemingly small shift moves a calculated ABV by about 0.4%, and it is the difference between recording your OG as 1.050 versus 1.053. Read the same hydrometer cold at 45°F and the correction flips negative, since cold wort is denser and the instrument reads slightly high.
What Affects Your Result
- Sample temperature — the dominant factor; the further from calibration temperature, the larger the correction, and it grows non-linearly as you get hot.
- Calibration temperature — 60°F on most North American hydrometers, 68°F on many European or lab models. Using the wrong one bakes in a constant error.
- Reading technique — read the bottom of the meniscus at eye level and spin off clinging bubbles, or you add a couple of points of error before correction even starts.
- Dissolved CO2 — gas bubbles on a fermenting sample buoy the hydrometer and read low; degas the sample first.
- Sugar vs. alcohol — this correction assumes a sugar solution; it does not adjust for the way a refractometer is skewed by ethanol after fermentation.
- Instrument calibration — check your hydrometer in distilled water at calibration temperature; if it does not read 1.000, note the offset and apply it too.
Frequently Asked Questions
Do I need to correct readings if my sample is at room temperature?
Within a few degrees of calibration temperature the correction is smaller than you can read off the scale, so you can skip it. By 70°F the error is about one point, and by 80°F it is two to three points — enough to matter for ABV and for judging whether fermentation has finished.
What temperature is my hydrometer calibrated to?
It is printed on the paper scale inside the tube. Most homebrewing hydrometers use 60°F (15.6°C); some European and lab-grade models use 68°F (20°C). Enter the value that matches your instrument.
Why does hot wort read lower than its true gravity?
Heat makes liquid less dense, so the hydrometer sinks deeper and shows a lower number. Cool the same wort and it contracts, gets denser, and the instrument rides higher. The correction reverses this effect mathematically.
Does temperature correction change my calculated ABV?
Yes. ABV is roughly (OG − FG) × 131.25, and a two- to three-point error on either reading shifts ABV by about 0.3–0.4%. Correcting both readings to the same calibration temperature gives the most reliable number.