27 C.F.R. § 30.64
This table provides a method for use in ascertaining the wine gallon (at 60 degrees Fahrenheit) and/or proof gallon contents of containers of spirits by multiplying the net weight of the spirits by the fractional part of a gallon per pound shown in the table for spirits of the same proof. Fractional gallons beyond the first decimal will be dropped if less than 0.05 or will be added as 0.1 if 0.05 or more.
Example. It is desired to ascertain the wine gallons and proof gallons of a tank of 190 proof spirits weighing 81,000 pounds.
81,000*0.14718=11,921.58=11,921.6 wine gallons.
81,000*0.27964=22,650.84=22,650.8 proof gallons.
This table may also be used for ascertaining the quantity of water required to reduce to a given proof. To do this, divide the proof gallons of spirits to be reduced by the fractional part of a proof gallon per pound of spirits at the proof to which the spirits are to be reduced, and subtract from the quotient the net weight of the spirits before reduction. The remainder will be the pounds of water needed to reduce the spirits to the desired proof.
Example. It is desired to ascertain the quantity of water needed to reduce 1,000 pounds of 200 proof spirits, 302.58 proof gallons, to 190 proof:
302.58 divided by 0.27964 equals 1,082.03 pounds, weight of spirits after reduction.
1.082.03 minus 1,000 equals 82.03 pounds, weight of water required to reduce to desired proof.
The slight variation between this table and Tables 2, 3, and 5 on some calculations is due to the dropping or adding of fractions beyond the first decimal in those tables. This table may also be used to determine the wine gallons (at 60 degrees Fahrenheit) of distilled spirits containing dissolved solids from the total weight of the liquid and its apparent proof (hydrometer indication, corrected to 60 degrees Fahrenheit). The proof gallons may then be found by multiplying the wine gallons by the true proof.
Temperature °F75.0° Hydrometer reading92.0° Apparent proof85.5° Obscuration0.5° True proof86.0°Example. 5,350 pounds of blended whisky containing added solids
5,350.0 lbs.*0.12676 (W.G. per pound factor for apparent proof of 85.5°)=678.2 wine gallons
678.2 W.G.*0.86=583.3 proof gallons
27 C.F.R. § 30.64
Sec. 201, Pub. L. 85-859, 72 Stat. 1358, as amended 1362, as amended ( 26 U.S.C. 5204 , 5211 )