pound-force per inch
Spring constantSurface tensionexact by definition
The pound-force per inch is the customary unit of spring rate, equal to 175.1268... N/m. The definition is exact because the pound-force and the inch are exactly defined, though the decimal does not terminate. A spring rated at 200 lbf/in compresses one inch under a 200 lbf load.
Watch out: Spring rate is not the same as spring load. A catalogue may list both a rate in lbf/in and a load at a given installed height in lbf, and they are different numbers describing different things. Note also that coil springs are only linear over part of their travel, so the rate applies within the working range and not at full compression.
| 1 lbf/in (Spring constant) | 175.12684 N/m |
| 1 lbf/in (Surface tension) | 175,126.84 mN/m |
The pound-force per inch is exactly 175.126835246... N/m. It is the standard reporting unit of North American peel and adhesion testing: pressure sensitive tape is specified in ounces or pounds per inch of width, and the quantity is a force per unit width, which is dimensionally a surface energy.