boils at 212 °F = 100 °C at 1 atm. The conversion formula is: or inversely as Other units Length 1 hand = 4 in = 1 U (rack unit) = 1.75 in = Volume 1 board-foot = 1 ft × 1 ft × 1 in = Mass 1 slug = 1 lbf⋅s2/ft ≈ 14.59390 kg Force 1 poundal = force to accelerate 1 pound mass 1 foot/second/second ≈ 0.138 Newtons. 1 kip = 1000 lbf ≈ Energy 1 foot-pound ≈ 1 British thermal unit (Btu) ≈ Power 1 horsepower ≈ 1 ton of refrigeration (12,000 Btu/h) = Pressure 1 inch of mercury = the pressure produced by 25.4 mm depth of mercury = 3,386.85 pascals (33.8685 hPa, millibars) 1 pound per square inch (psi) ≈ Torque 1 pound-foot ≈ Insulation 1 R-value (ft2⋅°F⋅h/Btu) ≈ 0.1761 RSI (K⋅m2/W) Various combination units are in common use; these are straightforwardly defined based on the above basic units. Sizing systems are used for various items in commerce, several of which are U.S.-specific: US standard clothing size American wire gauge is used for most metal wire. Scoop (utensil) sizes, numbered by scoops per quart Thickness of leather is measured in ounces, 1 oz equals . Bolts and screws follow the Unified Thread Standard rather than the ISO metric screw thread standard. Knitting needles in the United States are measured according to a non-linear unitless numerical system. Aluminum foil is measured in mils ( inch, or 0.0254 mm) in the United States. Cross-sectional area of electrical wire is measured in circular mils in the U.S. and Canada, one circular mil (cmil) being equal to (or ). Since this is so small, actual wire is commonly measured in thousands of a cmil, called either kcmil or MCM. The mil or thou is also sometimes used to mean thousandth of an inch. Sheet metal in the U.S. is commonly measured in gauge (not to be confused with the American wire gauge), which is derived from weight and thus differs by material. Nominal Pipe Size is used for the outside diameter of pipes. Below NPS14, the NPS number is not consistent with the pipe diameter in inches. Copper tubing, however, is measured in nominal size, inch less than the outside diameter. The Schedule system is used for standard pipe thicknesses. Alcohol content is frequently given in proof, 2 × alcohol by volume The cord is used for volume