Fixed physical constants
Each pair of units is linked by an exact ratio fixed by the definitions of the units: 1 lbf = 4.4482216152605 N and 1 ft = 0.3048 m make 1 ft-lb equal 1.3558179483 N·m, and 1 kgf = 9.80665 N with 1 dyn = 1e-5 N define the rest. Converting is one multiplication by the ratio in one direction and a division in the other, so the result is exact to the digits shown.