Professional Hydrometer Temperature Correction Calculator

Hydrometers read correctly only at their calibration temperature. Because water density varies with temperature, readings taken warmer or cooler than calibration must be corrected. This calculator applies a rigorous water-density model to adjust your observed reading to the calibration temperature, then reports corrected values in both SG and °Plato.

The Science Behind the Correction

Core equation (SG input)

SGcorr = (SGobs + offset) × f(Tsample) / f(Tcal)

Water SG polynomial (T in °F):

f(T) = 1.00130346 − 0.000134722124·T + 2.04052596×10⁻⁶·T² − 2.32820948×10⁻⁹·T³

Plato⇄SG transforms:

SG = 1 + P / (258.6 − (P/258.2)×227.1)
P  ≈ −616.868 + 1111.14·SG − 630.272·SG² + 135.997·SG³

Polynomial fit originates from CRC water data via Lyons (1992, HBD #963) and is widely used in brewing calculators; it captures the dominant temperature effect (water density) across typical wort ranges.

Variables Glossary

SGobs — observed specific gravity (hydrometer)
offset — instrument bias at calibration (e.g., +0.0020)
Tsample — sample temperature at reading
Tcal — hydrometer calibration temperature (e.g., 60 °F, 68 °F, or 20 °C)
P — degrees Plato

Worked Example

1Observed: 1.050 at 80 °F; hydrometer 68 °F; offset 0.

2Compute f(80) and f(68); ratio ≈ 1.0023.

3SGcorr = 1.050 × 1.0023 = 1.052 (≈ +2 points).

When is Correction Critical?

  • High differentials (e.g., hot wort vs 60 °F calibration)
  • Commercial QC and regulatory contexts
  • ABV calculations where ±0.001 SG è significativo

Authoritative Sources & Further Reading

  • Lyons, C. (1992). Hydrometer Temperature Corrections, Home Brew Digest #963 — CRC-based cubic valid 0–212 °F. brewery.org · hbd.org
  • Brewer’s Friend. Hydrometer Temperature Adjustment (overview & usage). brewersfriend.com
  • Vinolab. Hydrometer Temperature Correction (explicit polynomial with coefficients). vinolab.hr
  • ASBC Methods (Wort: SG/Extract; hydrometer standardized at 20 °C for °Plato). asbcnet.org
  • BeerSmith (calibration temps 60 °F / 68 °F & practical guidance). beersmith.com

Nota: alcuni strumenti °Plato industriali riportano esplicitamente 20 °C come standard (ASBC).

FAQ

Is the correction valid for high-gravity wort?

Sì. L’effetto principale è la densità dell’acqua; il rapporto f(T) è robusto nel range birrario. Evita extrapolazioni fuori 0–90 °C.

Come trovo la calibrazione del mio idrometro?

È stampata sullo stelo/manale; tipicamente 60 °F o 68 °F (SG) e 20 °C (°Plato/ASBC).