Foot pounds to newton meters (lb-ft to N·m)

One pound-foot is exactly 1.3558179483314004 newton-meters, which is 4.4482216152605 times 0.3048: the pound-force and the foot, both exact by definition, multiplied together.

Worked through: 35 lb-ft x 1.35581795 = 47.4536 N·m.

Going the other way, one newton-meter is 0.7375621493 pound-feet.

For mental arithmetic: Multiply by 1.36: add a third, then a bit more.

The direction a European service manual demands when the workshop's wrench is imperial. The common specs are worth memorizing as a block: 20 lb-ft is 27 N.m, 50 is 68, 80 is 108, 100 is 136. Note that pound-inches are a separate unit a twelfth the size and small fasteners are specified in them. A torque of 35 given without a unit is 35 lb-in on a valve cover and 35 lb-ft on a lug nut, and mistaking one for the other either shears the bolt or leaves the wheel loose.

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