Pound-foot

Unit

The value in Système International (SI) units is given by multiplying the following exact factors:

• One pound (mass) = 0.45359237 kilograms;
• Standard gravity = 9.80665 m/s²; and
• One foot = 0.3048 m.

This gives the exact conversion factor,

• One pound-foot = 1.3558179483314004 newton metres.

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.

Despite this, in practice torque units are commonly called the foot-pound (denoted as either lb-ft or ft-lb) or the inch-pound (denoted as in-lb). Practitioners depend on context and the hyphenated abbreviations to know that these refer to neither energy nor moment of mass (as the symbol ft-lb rather than lbf-ft would imply).

Similarly, a pound-inch (or inch-pound) is the torque of one pound of force applied to one inch of distance from the pivot, and is equal to 1⁄12 lbf⋅ft (0.1129848 N⋅m). It is commonly used on torque wrenches and torque screwdrivers for setting specific fastener tension. An ounce-inch (or inch-ounce) is a smaller unit, equal to 1⁄16 of a pound-inch, or 0.7062 newton-centimetres (7.062 millinewton-metres).