Newton meters to foot pounds (N·m to lb-ft)

One newton-meter is 0.73756214927727 pound-feet, and the factor is exact in principle: a pound-force is exactly 4.4482216152605 newtons and a foot exactly 0.3048 meters, both fixed by definition rather than measured. It does not land anywhere round.

Worked through: 80 N·m x 0.737562149 = 59.005 lb-ft.

Going the other way, one pound-foot is 1.355817948 newton-meters.

For mental arithmetic: Multiply by 0.74: three quarters, less a little.

The conversion every torque wrench crosses. Two things to get right. First the name: this is pound-FEET, and American practice writes torque as lb-ft and energy as ft-lb precisely so the two are distinguishable, because a newton-meter and a joule are dimensionally identical and conceptually different: torque is force applied at a distance perpendicular to it, and energy is force applied through a distance. Tightening a bolt to 100 N.m does not transfer 100 J. Second the precision: a click wrench is typically accurate to about 4%, so converting a spec of 90 N.m to 66.38 lb-ft and setting 66.38 implies a precision the tool does not have. Round to the nearest whole number and use the manufacturer's unit where you can.

Precision is worth matching to the input. A measurement given as 10 N·m carries one or two significant figures, and reporting its conversion to six implies a precision the original never had.