27 CFR § 19.226 - Gauges for tax determination.
There are several acceptable methods that a proprietor may use when gauging spirits for tax determination.
(a) Cases. If spirits are withdrawn from the bonded premises in cases, the proprietor must gauge the spirits based on the contents of the cases. The proprietor will determine the number of proof gallons of spirits in cases as provided in part 30 of this chapter. The proprietor must convert metric units of measure to U.S. units according to § 19.579.
(b) Packages. If spirits are withdrawn from the bonded premises in packages on the basis of an individual package gauge, each package must be gauged unless the tax is to be determined on the production or filling gauge. When gauging the packages, the proprietor must prepare a package gauge record as specified in § 19.619 and attach it to the record of tax determination that is required by § 19.611.
(c) Tanks. The proprietor must use weight, or an accurate mass flow meter and proof as prescribed in §§ 19.284 and 19.285, to gauge bulk spirits in tanks that are to be withdrawn on determination of tax. The proprietor must record the elements of the gauge on the record of tax determination. As an alternative, the proprietor may record gauge elements on a separate gauge record, and attach the gauge record to the record of tax determination.