In the "engineering" systems (middle column), the weight of the mass unit (pound-mass) on Earth's surface is approximately equal to the force unit (pound-force). This is convenient because one pound mass exerts one pound force due to gravity.

Is pound mass and pound force the same?

One of the greatest sources of confusion in the Imperial (or U.S. Customary) system of measurement is that both mass and force are measured using the same unit, the pound. The differentiate between the two, we call one type of pound the pound-mass (lbm) and the other the pound-force (lbf).

Is lbf a mass?

The pound mass, abbreviated lbm, is a unit of mass which is defined as 0.453 592 37 kilogram. The pound force unit, abbreviated lbf or simply lb, is a unit of force equal to that exerted by one pound mass under the gravitational acceleration at the earth's surface.