Free tools for winemakers
Hydrometer temperature correction calculator
Correct a hydrometer reading for temperature
Corrected reading
Type the reading, the sample temperature and the calibration temperature.
Printed on the hydrometer. Most are 20 °C; older and US ones 15.56 °C (60 °F).
For hydrometers only. A refractometer with automatic temperature compensation (ATC) corrects for temperature itself, so its reading needs no correction here.
For the best accuracy, read near the calibration temperature. The correction is close, not exact, and less exact the sweeter the sample and the further its temperature is from the calibration temperature. Bring the sample close to the calibration temperature (printed on the hydrometer) before you read it.
How do we calculate this?
The exact formulas used in this tab:
What this calculator does
Corrects a hydrometer reading for the temperature of the sample. Type the reading in any sugar scale (Brix, SG, Baumé, Oechsle or KMW) and get it back corrected, in the same scale.
- A hydrometer reads true only at the temperature it was calibrated at: usually 20 °C, or 15.56 °C (60 °F) on older and US ones.
- Warm must is less dense, so it reads low; cold must reads high.
The formula
Any reading is converted to SG first, and back to its own scale afterCorrected SG = measured SG × f(sample T) ÷ f(calibration T)f(T) = 1.00130346 − 0.000134722124·T + 0.00000204052596·T² − 0.00000000232820948·T³T in °F: °F = (°C × 9/5) + 32f(T) follows water: a sweet must expands a little more, so a warm sample is slightly under-correctedSample temperature up to 35 °CFor hydrometers only: refractometers with ATC correct for temperature themselves
Worked example
A reading in SG
- Reading: 1.090 SG
- Sample at 30 °C (86 °F)
- Calibrated at 20 °C (68 °F)
- Factor at the sample temperature f(86) = 1.003328
- Factor at calibration f(68) = 1.000846
- Correction 1.003328 ÷ 1.000846 = 1.00248
- Corrected reading 1.090 × 1.00248 = 1.0927 SG
1.0927 SG: the warm sample read 2.7 points low
A reading in Brix
- Reading: 22 °Bx
- Sample at 30 °C
- Calibrated at 20 °C
- The reading in SG 22 °Bx = 1.0920 SG
- The same correction 1.0920 × 1.00248 = 1.0947 SG
- Back to Brix 1.0947 SG = 22.6 °Bx
The true reading is 22.6 °Bx
Questions
Why does a warm sample read low?
Liquid expands as it warms, so the same must is a little less dense. The hydrometer sinks deeper and shows less sugar than is really there. A must at 30 °C on a 20 °C hydrometer reads about 0.6 °Bx low, enough to throw off a chaptalization or a potential alcohol figure.
Do I need this for a refractometer?
Usually not. Most refractometers have automatic temperature compensation (ATC) and correct for temperature themselves. This calculator is for hydrometers.
What temperature is my hydrometer calibrated at?
It is printed on the hydrometer, often on the paper scale inside it. Most wine hydrometers are calibrated at 20 °C; older ones and many sold in the US at 15.56 °C, which is 60 °F. Pick the matching button, or type another figure.
How accurate is the correction?
Close enough for everyday cellar work, but it is an approximation. The curve behind it is for water, and a sugary must expands a little more with heat. So the sweeter the sample and the further it is from the calibration temperature, the more the correction falls short. For the most accurate reading, bring the sample close to the calibration temperature before you read it. The calculator accepts samples from 0 °C to 35 °C; past that the gap is too big to trust.