1 · Input data
A conversion between the units a structural engineer actually types, for length, area, volume, mass, force, pressure and stress, moment, moment of inertia, section modulus and temperature. No code governs a unit conversion, so this page cites no clause. Every factor is derived from a defining relation — 1 in = 25.4 mm, 1 lb = 0.45359237 kg, g0 = 9.80665 m/s2, 1 ft = 12 in, 1 yd = 3 ft, 1 mi = 5280 ft, 1 acre = 4840 yd2, 1 US gal = 231 in3, 1 L = 1 dm3, 1 short ton = 2000 lb, 1 slug = 1 lbf·s2/ft, 1 kgf = 1 kg × g0, 1 lbf = 1 lb × g0 — and the relation behind each factor is printed beside it. The convention followed is the one NIST SP 811 (the US guide to the SI) and the SI brochure (BIPM, 9th edition) use: state which relations are exact by definition and derive the rest from them. The page prints the converted value and the factor it used, so the arithmetic can be checked by hand. It refuses the two conversions that are not conversions at all: mass is not force, and a section modulus is not a volume. A conversion between two units of one quantity runs through the SI base unit, so it is exact by construction and a value converted out and back is the value again. Press Convert when the card is complete.
The two unit dropdowns are filled from the quantity you choose, because a unit is only a unit of a quantity. That is also why the page keeps mass and force in separate families: a dropdown that offered “lb” and “N” at once would invite exactly the conversion this page exists to refuse.
2 · Solution
No solution yet — complete every input in the card above and press Convert. This card stays empty until a solution is computed, and it is emptied again the moment any input changes, so a displayed solution always belongs to the inputs on screen.