27 CFR § 53.115 - Computation of tax.
(a) Tax based on price. Tax liability incurred on the use of an article shall be computed on the price at which such or similar articles are sold in the ordinary course of trade by manufacturers, producers, or importers thereof and in the absence of special arrangements. For additional provisions applicable in computing the tax in the case of the use of an article by a manufacturer and producer who purchased the article free of tax under section 4221(a)(1) of the Code for use by him in further manufacture, see section 4223(b) of the Code and the regulations thereunder (§ 53.143).
(b) Articles regularly sold by manufacturer. If the manufacturer, producer, or importer of an article regularly sells such articles at wholesale in arm's length transactions, tax liability on his use of any such article shall be computed on his lowest established wholesale price for such articles in effect at the time of the taxable use. In establishing such price, there shall be included and excluded, as applicable, the charges and readjustments specified in sections 4216(a) and 6416(b)(1) of the Code, as in effect at the time tax liability on the use of the article is incurred, and the regulations thereunder contained in this subpart and subpart L (§§ 53.91–53.94 and 53.173–53.176). If the manufacturer, producer, or importer of an article does not regularly sell such articles at wholesale in arm's length transactions, a constructive price on which the use tax shall be computed will be determined by the appropriate TTB officer. This price will be established after considering the selling practices and price structures of manfacturers, producers, and importers of similar articles.
(c) Articles governed by section 4218(a) used in manufacture of nontaxable combination articles. If the manufacturer, producer, or importer of an article to which section 4218(a) of the Code applies does not regularly sell such article separately but uses it as material in the manufacture or production of, or as a component part of, a nontaxable combination article consisting of a taxable and nontaxable article, liability for tax on his use shall be computed on the constructive price of the taxable article at the time of use. To determine the constructive price of the taxable article in such case, the combination article is considered to be composed of:
(1) Parts used exclusively in the functioning of the taxable article in the combination;
(2) Parts used exclusively in the functioning of the nontaxable article in the combination, and
(3) Parts, called common parts, which serve a dual function in connection with the parts in both paragraphs (c) (1) and (2) of this section.