To convert newton-meters to pound-feet, divide the N·m value by approximately 1.355818. Equivalently, multiply it by approximately 0.7375621. For example, 25 N·m is about 18.44 lbf·ft. To go the other way, multiply pound-feet by 1.355818.
The same torque can also be expressed in pound-inches. Keep the complete unit beside every number: a value in lbf·in is twelve times the numerical value in lbf·ft. This guide brings all three units together, using abstract quantities rather than settings for any particular object.
Read the unit before choosing a factor
N·m means newton-meter: the symbol N represents the newton, a unit of force, and m represents the meter. The centered dot means multiplication. You may also see a space, as in N m. In contrast, lowercase nm means nanometer, a very small unit of length. Capitalization changes the meaning.
Pound-feet here means pound-force feet, written lbf·ft. Pound-inches means pound-force inches, written lbf·in. The f makes the force meaning explicit. A pound of mass, written lb, describes a different quantity. A mass conversion from kilograms to pounds therefore cannot supply a torque conversion.
Searches and informal labels often use “ft lbs,” “ft-lb,” or “lb-ft.” First confirm that the surrounding text describes torque. For your own calculation, rewriting the label as lbf·ft removes the ambiguity about force. Do not rewrite a slash as a multiplication dot: lbf/ft means force per length, not torque.
The conversion factors in one place
NIST’s Appendix B.8 conversion table lists approximately 1.355818 N·m per lbf·ft and 0.1129848 N·m per lbf·in. These displayed decimal factors are rounded. Their reciprocals provide the conversions from newton-meters.
- N·m to lbf·ft: divide by 1.355818.
- lbf·ft to N·m: multiply by 1.355818.
- N·m to lbf·in: divide by 0.1129848.
- lbf·in to N·m: multiply by 0.1129848.
- lbf·ft to lbf·in: multiply by exactly 12.
- lbf·in to lbf·ft: divide by exactly 12.
The direct N·m-to-lbf·in multiplier is approximately 8.850748. Using division by the listed NIST factor avoids having to copy a separately rounded reciprocal. Either approach is reasonable when the final result is rounded consistently.
Convert newton-meters to pound-feet
Take an abstract torque of 25 N·m. Divide 25 by 1.355818 to obtain 18.439053… lbf·ft. Rounded to two decimal places, that is 18.44 lbf·ft. The quantity has stayed the same; only the numerical value and its unit have changed.
For a smaller example, 12 N·m ÷ 1.355818 gives 8.850745… lbf·ft, or 8.85 lbf·ft. For positive values, the pound-feet number should be smaller than the newton-meter number because one pound-foot is larger than one newton-meter. An answer larger than 12 would be a reason to check the operation.
You can also write the first calculation as 25 N·m × (1 lbf·ft / 1.355818 N·m). The N·m units cancel, leaving lbf·ft. This unit-cancellation method is useful when a conversion factor is written in the opposite direction from the one you need.
Reverse the calculation without changing the factor
Suppose the starting quantity is 18 lbf·ft. Multiplying 18 by 1.355818 gives approximately 24.404724 N·m, or 24.40 N·m to two decimal places. The numerical value increases in this direction.
A round-trip check returns that unrounded result to the original unit: 24.404724 ÷ 1.355818 = 18. Keep the intermediate digits for this check. If you instead convert the rounded 24.40 N·m back, the result is only approximately 18, which is expected after discarding decimal places.
Use the same source factor in both directions. Multiplying by one heavily rounded shortcut and dividing by a different shortcut can introduce a discrepancy that looks like an arithmetic error. There is no benefit in reporting all the digits a calculator displays when the starting quantity is only approximate.
Include pound-inches and the factor-of-12 check
An abstract value of 60 lbf·in is exactly 5 lbf·ft because 60 ÷ 12 = 5. Using the pound-inch factor, 60 × 0.1129848 gives approximately 6.779088 N·m, or 6.78 N·m. Using the pound-foot route, 5 × 1.355818 gives 6.77909 N·m. Both round to the same answer.
That tiny difference comes from the independently rounded decimal factors, not from the relationship between feet and inches. The factor of 12 is exact. For a chain of calculations, choose one route and retain its intermediate values rather than switching between rounded results.
In the opposite direction, 12 N·m ÷ 0.1129848 gives approximately 106.208977 lbf·in, or 106.21 lbf·in. Compare this with the earlier 8.850745… lbf·ft result: multiplying it by 12 also gives 106.21 after rounding. A result near 8.85 labeled pound-inches would reveal a missing factor of 12.
Torque, energy and power use different descriptions
Torque describes a turning effect. Energy describes an amount of work or energy transfer, while power describes a rate of energy transfer. The NIST table of SI derived units gives the joule as N·m and the watt as J/s. Sharing a dimensional expression does not make torque and energy interchangeable quantities.
Use N·m for torque rather than relabeling a torque number in joules. NIST lists foot pound-force to joules separately from pound-force foot to newton-meters. Reading the quantity being described matters more than relying on the order of the words alone.
A torque value also cannot be converted directly to horsepower without additional information about rotational speed. If the quantity you are comparing is already power, the kilowatts-to-horsepower guide covers those units separately.
Keep a clear record of the answer
Write down the original quantity, the factor used and the final unit. Round at the end, choosing decimal places that suit the precision of the original value. Two decimal places in these examples make the arithmetic easy to compare; they are not a universal precision requirement.
Before copying a result, check three details: uppercase N in N·m, force identified by lbf, and feet versus inches. Those checks distinguish a notation mistake from a calculation mistake. For handwritten calculations, you can browse plain notebooks on Amazon.
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