Free tool

TTB Gauging Calculator (Temperature Correction)

Hydrometer readings must be corrected to the standard temperature of 60F. This tool applies TTB Gauging Manual Table 1 to convert your observed proof at a given temperature to true proof. It uses the same audited Table 1 lookup as Spirit Sight.

proof
F

The formula

true proof at 60F via TTB Gauging Manual Table 1 (interpolated by temperature and proof)

A worked example

A hydrometer reading of 102.4 proof taken at 71 degrees F is not the true proof; spirit expands when warm. Enter the indicated proof and temperature and the calculator interpolates TTB Gauging Table 1 to return the true proof at 60 degrees F, the number your records and reports must carry.

Doing this math barrel by barrel? The platform runs the same calculation on every record automatically, reconciled against the books. See it live.

27 CFR 30.61 (TTB Gauging Manual Table 1); proof to the nearest 0.1 per 27 CFR 30.31. This tool uses the same calculation as the Spirit Sight platform. It is general information, not tax or legal advice.

Why do you temperature-correct proof?
Alcohol expands with heat, so a hydrometer reads differently at different temperatures. TTB requires proof to be determined at 60F, so a reading taken warmer or cooler must be corrected before it is used for tax or reports.
What table does the TTB use for proof correction?
Gauging Manual Table 1, incorporated by reference in 27 CFR 30.61. This tool interpolates that table by observed proof and temperature.
What proof precision does TTB require?
Proof is determined to the nearest 0.1 degree under 27 CFR 30.31. This calculator returns the corrected proof at that precision.
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