N.H. Rev. Stat. Ann. § 438:2

The system of weights and measures in customary use in the United States and the metric system of weights and measures are jointly recognized, and either one or both of these systems shall be used for all commercial purposes in the state of New Hampshire. The definitions of basic units of weight and measure, the tables of weight and measure, and weights and measures equivalents as published by the National Institute of Standards and Technology are recognized and shall govern weighing and measuring equipment and transactions in the state.