Pound-feet to newton-meters converter

How to convert ft-lbs to Nm

Multiply pound-feet by 1.3558179483314004 to get newton-meters. So 80 lb-ft is 108.47 N·m, 25 lb-ft is 33.90 N·m and 200 lb-ft is 271.16 N·m. Use it to set a metric torque wrench from a US service manual or to compare engine torque figures.

Why the factor is 1.3558

One pound-foot is one pound-force (4.4482216152605 N) applied one foot (exactly 0.3048 m) from the pivot. The product, 1.3558179483314004 N·m, is exact (NIST SP 811, Appendix B; pound-force footnote).

For a mental estimate, multiply by 1.36 (0.3% high) or add a third (1.7% low): 80 lb-ft comes out as 108.8 or 106.7 N·m.

lb-ft to Nm chart

Convert the tolerance too

A spec of 80 ± 0.5 lb-ft becomes 108.47 ± 0.68 N·m. The tolerance uses the same factor: 0.5 × 1.3558179483314004 = 0.6779089741657002 N·m.

Round only the final figures, and only as far as the wrench scale can be read.

Inch-pound specs

Small fasteners are often given in lbf·in (in-lb). Divide by 12 to get pound-feet first: 100 lbf·in is 8.33 lb-ft, or 11.30 N·m.

Reading that spec as 100 lb-ft would give 135.58 N·m, twelve times the intended torque.

Foot-pounds of energy

Foot-pounds also measure work and energy, for example the muzzle energy of an air rifle. The same factor converts them to joules, the SI unit of energy: 12 ft·lbf is 16.27 J.

Torque and energy share the factor but not the meaning, so write torque in N·m and energy in J.

Common mistakes

• Dividing by 1.3558. That converts the other way and turns 80 lb-ft into 59.00 instead of 108.47. The N·m figure is always the larger one.
• Using a force as a torque. Pounds-force alone are not torque; multiply by the lever length in feet first. A 50 lbf push on an 18-inch (1.5 ft) bar gives 75 lb-ft, or 101.69 N·m.

Related torque conversions

The Nm to ft-lbs converter goes the other way. The torque converter handles lbf·in and kgf·m, the energy converter covers joules, and the horsepower calculator combines torque with rpm.