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