27 C.F.R. § 30.62
The wine and proof gallon content by weight and proof of packages of distilled spirits usually found in actual practice will be ascertained from this table. The left-hand column contains the weights. The true percent of proof is shown on the heading of each page in a range from 90 degrees to 200 degrees. Under the true percent of proof and on the same horizontal line with the weight will be found the wine gallons (at 60 degrees Fahrenheit) and the proof gallons respectively. Where either the weight or the proof of a quantity of spirits is beyond the limitations of this table, the number of proof gallons may be ascertained by reference to Table 3. This table may also be used to ascertain the wine gallons (at 60 degrees Fahrenheit) and proof gallons of spirituous liquor containing dissolved solids where the weight, apparent proof (hydrometer indication corrected to 60 degrees Fahrenheit), and obscuration factor have been determined.
Example. 334 lbs. of distilled spirits.
Apparent proof-96.0°.
Obscuration-0.8°.
True Proof 96.0°+0.8°=96.8°.
334 lbs. at 96.0° apparent proof=42.8 wine gallons.
42.8 wine gallons*96.8°=41.4 proof gallons.
In addition this table may be used to obtain the wine gallons, at the prevailing temperature, of most liquids within the range of the table, from the weight of the liquid and the uncorrected reading of the hydrometer stem. An application of this would be in determining the capacity of a package.
Example. It is desired to determine, or to check the rated capacity of a package having a net weight of 395 pounds when completely filled with spirits having an uncorrected hydrometer reading of 113.0°. The full capacity of the package, 51.5 wine gallons, would be found by referring to the table at 395 pounds and 113° proof (hydrometer reading).
27 C.F.R. § 30.62
Sec. 201, Pub. L. 85-859, 72 Stat. 1358, as amended, 1362, as amended ( 26 U.S.C. 5204 , 5211 )