A torque converter changes a twisting force between units — newton-metres to pound-feet, or pound-inches to newton-centimetres. Torque is force applied at a distance from a pivot, so its units are always a force multiplied by a length. This tool covers N·m, lb·ft, lb·in, kgf·m, N·cm and oz·in.
The formula. Every value passes through the newton-metre — one newton applied one metre from the axis. The factors are 1 lb·ft = 1.355818 N·m, 1 lb·in = 0.112985 N·m (one twelfth of a pound-foot), 1 kgf·m = 9.80665 N·m and 1 oz·in = 0.007062 N·m. Because torque is force × distance, the same bolt spec can be met with less force on a longer wrench.
Worked example. A wheel-nut spec of 100 N·m is 100 ÷ 1.355818 = 73.76 lb·ft. A small electronics screw at 5 lb·in is 5 × 0.112985 = 0.565 N·m. And an engine quoted at 250 N·m of torque produces about 184 lb·ft — the figure a US specification sheet would print for the same engine.
Where it's used. Every torque wrench is calibrated in one system and every workshop manual in whichever the manufacturer chose, so this is one of the most practical conversions in the garage — and over-tightening because of a unit mix-up shears bolts. Engine specifications, bicycle components, furniture assembly instructions and electronics assembly (oz·in for small fasteners) all use different units for the same quantity. Note that torque shares its dimensions with energy but is never expressed in joules, precisely to keep the two ideas apart.