N.H. Rev. Stat. Ann. § 261:142

In the computation of fees, gross weight shall be the actual weight of said vehicle in pounds plus the manufacturer's rated load capacity in the case of freight or merchandise vehicles, and, in the case of passenger vehicles, shall be the actual weight of said vehicle plus the sum of the adult seating capacity multiplied by 150 pounds. The next larger 100 pounds shall be used in computing fees.