Gravity Correction Calculator - Brewing, Bouguer & Mass

Correct brewing hydrometer SG, calculate free-air and Bouguer anomalies, or adjust indicated mass for local gravity and air buoyancy with visible terms.

Brewing Temperature Correction Formula

The following formula is a common approximation used to temperature-correct a hydrometer gravity reading when working in Specific Gravity (SG). The calculator converts °Plato to SG (if needed), applies the correction, and then converts back to °Plato.

SG corr = SGₘₑₐₛ \times (ρ w (T ref)) / (ρ w (Tₘₑₐₛ))

Variables:

SG_corr is the temperature-corrected specific gravity (dimensionless)
SG_meas is the measured specific gravity at the sample temperature (dimensionless)
ρ_w(T) is the density of pure water at temperature T (kg/m³)
T_meas is the sample temperature (°C)
T_ref is the instrument calibration/reference temperature (°C)

Note: hydrometer temperature correction can be instrument-specific (and may include glass expansion and wort thermal expansion). For best accuracy, use the manufacturer’s correction table. This calculator uses a water-density-based approximation that is often adequate for typical brewing temperature ranges.

What is Gravity Correction?

“Gravity correction” can mean different things depending on context. In brewing, it usually means adjusting a hydrometer gravity reading for temperature differences from the hydrometer’s calibration temperature (commonly 20°C or 60°F). In geophysics, gravity corrections are applied to measured gravitational acceleration to help compute anomalies (such as free-air and Bouguer anomalies). In mass metrology, gravity correction adjusts an indicated mass to account for local gravitational acceleration (and sometimes air buoyancy).

How to Calculate Corrected Gravity?

The following steps outline how to calculate a brewing temperature-corrected gravity reading.

Measure the gravity as Specific Gravity (SG) or °Plato.
Record the sample temperature (T_meas) and the hydrometer’s calibration/reference temperature (T_ref), using consistent units (e.g., °C).
If your measurement is in °Plato, convert it to SG (the calculator does this automatically).
Compute the density of pure water at T_meas and T_ref, then apply: SG_corr = SG_meas × ρ_w(T_ref)/ρ_w(T_meas).
If desired, convert SG_corr back to °Plato.
Check your answer with the Brewing tab in the calculator above.

Example Problem:

Use the following variables as an example problem to test your knowledge.

observed gravity (measured) = 12.5 °Plato

sample temperature (T_meas) = 25 °C

calibration temperature (T_ref) = 20 °C