The Proper Way To Express Torque Units Is Ft·lbf Or N·m And ... - LinkedIn

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New Years Resolution #1. We will make an effort to educate the masses on the proper way to express torque units.

Looking at several scopes, manufacturer's specification sheets and other sources, as a metrology community, we do not always express units of torque properly.

Torque = Force * Length

This means N·m is acceptable, lbf·in is acceptable, lbf·ft is acceptable.

ft·lbf or in·lbf is is not the conventional method for expressing torque. You will not find this as an accepted expression of torque in the ASTM torque standard (ASTM E2428) or any NIST handbook. You will find several manufacturers expressing torque the improper way.

The foot-pound force (symbol: ft. · lbf) is a unit of work or energy in the Engineering and Gravitational Systems in United States customary and imperial units of measure. It is the energy transferred on applying a force of one pound-force (lbf) through a linear displacement of one foot.

A pound-foot (lbf·ft) is a unit of torque (a pseudovector). One pound-foot is the torque created by one pound force acting at a perpendicular distance of one foot from a pivot point. The name "pound-foot", intended to minimize confusion with the foot-pound as a unit of work, was apparently first proposed by British physicist Arthur Mason Worthington.

One pound-foot is approximately 1.355818 newton meters.

Conversion per NIST sp811

The improper use of torque units can easily be corrected. When you see manufacturers using ft·lbf on a torque specification, let them know the proper way to express torque is Force times Length.

So remember to express torque in lbf·ft, lbf·in, lbf·oz, or N·m.

Morehouse currently has the second most accurate torque machine in the world. We can achieve measurements better than 0.0025 % of applied torque from 0.5 through 1475 lbf·ft.

More information on our torque calibration services can be found here.

written by Henry Zumbrun

www.mhforce.com

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Share 19 10 Comments Jonson Liu 2y

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I am reading your BMS book. May I have the honor to connect with you?

Like Reply 1 Reaction Lowell Steele 4y

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I'm sure this is a typo, since it's expressed correctly in the article, but the article's headline leads off with the unit of measurement backwards (actually contradicting itself). As noted in the article, it is N·m or lbf·ft of torque, not ft·lbf.

Like Reply 2 Reactions 3 Reactions Curtis Thomas 4y

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Part of what’s screwy is the physics. The twist at a fixed point is the same if a 100 pound weight was hung from a one foot bar or if a 100 foot bar had a one pound weight hung from it.

Like Reply 1 Reaction Geoffrey H. Goldberg 8y

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Here is a useful conversion: 1 lb-ft = 1 ft-lb. Do the math.

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