27 C.F.R. § 30.51
Where the quantity of spirits (including denatured spirits) in bulk is to be determined by volume as authorized by this chapter, the measurement shall be made in tanks, by meters as provided in 27 CFR part 19, or by other devices or methods authorized by the appropriate TTB officer, or as otherwise provided in this chapter, or such measurement may be made in tank cars or tank trucks if calibration charts for such conveyances are provided and such charts have been accurately prepared, and certified as accurate, by engineers or other persons qualified to calibrate such conveyances. Volumetric measurements in tanks shall be made only in accurately calibrated tanks equipped with suitable measuring devices, whereby the actual contents can be correctly ascertained. If the temperature of spirits (including denatured spirits) is other than the standard of 60 degrees Fahrenheit, gallonage determined by volumetric measurements shall be corrected to the standard temperature by means of table 7. In the case of denatured spirits, the temperature-correction factor for the proof of the spirits used in denaturation will give sufficiently accurate results, except that the temperature-correction factor used for specially denatured spirits, Formula No. 18, should be that given in table 7 for 100 proof spirits. When the quantity of spirits, in wine gallons, has been determined by volumetric measurement, the number of proof gallons shall be obtained by multiplying the wine gallons by the proof of the spirits as determined under § 30.31 .
Example. Gauge glass reading inches-88.
Wine gallons per inch-48.96.
Temperature °F-72.
Proof of spirits-86.8.
Temperature correction factor (Table 7)-0.995.
48.96 W.G.*88=4308.48 wine gallons.
4308.48 W.G.*0.995=4286.94 wine gallons.
4286.94 W.G.*0.868=3721.06392=3721.1 proof gallons.
27 C.F.R. § 30.51
Sec. 201, Pub. L. 85-859, 72 Stat. 1358, as amended ( 26 U.S.C. 5204 )