Miss. Code Ann. § 27-25-5

The measure of this tax is the quantity of timber or timber products at the date of severance or production. If the timber is manufactured into lumber and the tax cannot be computed from weight or measured volume, because no record is used or available or the producer or purchaser does not maintain adequate records to show the measure of the tax by weight or measured volume, the tax shall be paid upon the number of board feet of lumber manufactured from the timber. The commissioner may prescribe rules and regulations for ascertaining the quantity of timber or timber products for the purposes of this article.