Introduction
Torque is rotational force — how hard something twists. The SI unit is the newton-meter (N·m); US mechanics use foot-pounds (ft·lb), and precision assembly (electronics, dental) uses inch-pounds or newton-centimeters. Wrench specs matter for everything from lug nuts to jet-engine fasteners — too little and the joint loosens, too much and the bolt strips or breaks.
Why torque units exist and how they diverged
Torque equals force times lever arm. A 10 N force on a 1-meter-long wrench handle creates 10 N·m of torque at the fastener. Cars specify lug nut torque in the manual: typical US cars are 100-120 ft·lb (135-163 N·m), European cars 110-140 N·m. Under-torqued lugs loosen and wheels fall off; over-torqued lugs strip the studs or warp brake rotors.
Foot-pound vs pound-foot — they're the same unit for torque but the abbreviation 'ft·lb' or 'lb·ft' is contested. ASME standards prefer 'lbf·ft' (pound-force-foot). In practice, Americans say 'foot-pounds' for torque and 'pound-feet' is less common but means the same thing.
How to convert torque
Foot-pounds to newton-meters: multiply by 1.356. Newton-meters to foot-pounds: multiply by 0.738. Inch-pounds to newton-meters: multiply by 0.113. Inch-pounds to foot-pounds: divide by 12.
Units supported by this torque calculator
- Newton-meters
- Foot-pounds
- Inch-pounds
- Kilogram-force meters
Common torque conversion mistakes
- Foot-pound vs pound-foot. For torque, same unit, different word order. Avoid 'ft-lb' (torque) vs 'lb-ft' (torque) confusion by spelling out 'foot-pound of torque.'
- Dry vs lubricated threads. Torque specs usually assume dry or lightly oiled threads. A well-lubricated thread reaches the same clamp load at 20-30% less torque. Apply oil only when the spec calls for it, or you'll over-stretch the fastener.
- Click torque wrench calibration. These drift over time. For critical work, calibrate annually or when accuracy matters (cylinder head bolts, wheel studs).
- Extension on a torque wrench. Adds leverage; changes the effective torque at the fastener. Torque sticks or calibrated extensions exist for this; random socket extensions don't.
- Inch-pounds vs foot-pounds. 1 ft·lb = 12 in·lb. A 100 in·lb spec is 8.3 ft·lb, not 100 ft·lb. Easy to miss on small fasteners.
Real-world torque examples
- Hand-tight screw: ~1-3 N·m (~10-30 in·lb).
- Spark plug: 25-35 N·m (18-26 ft·lb).
- Car lug nut (passenger car): 110-140 N·m (80-100 ft·lb).
- Truck lug nut: 170-200 N·m (125-150 ft·lb).
- Bicycle crank bolt: 50-60 N·m (37-44 ft·lb).
- Cylinder head bolt (car): 80-120 N·m with torque angle.
- F1 car wheel nut (center-lock): 600+ N·m.
- Jet engine turbine bolt: 500-2,000 N·m.
Tips for accurate torque conversion
- Always use a torque wrench for critical fasteners. Lug nuts, engine bolts, suspension components.
- Tighten in pattern (star pattern on 4-5 lug wheels, diagonal on cylinder head bolts) in stages — 50%, 75%, 100% of final torque.
- For small electronics assembly, inch-pounds or newton-centimeters. Over-torquing a 2 mm screw strips the threads instantly.
Related: Force Converter · Power Converter · Angle Converter.