How to use the Torque Calculator
- For a lever or fastener, enter the applied force and the distance from the axis.
- For a rotating machine, enter power and rotational speed instead.
- Check the units — newton-metres and pound-feet differ by a factor of about 1.356.
- Compare the result against the manufacturer's specified torque, not a general table.
How the calculation works
Torque is the cross product of force and radius, so only the component of force perpendicular to the lever contributes. Pulling a spanner at an angle produces less torque than the same force applied square to it, and doubling the lever length doubles torque for the same hand force — the reason a breaker bar works.
For rotating machinery, torque and power are linked through angular velocity: power is torque times radians per second. That relationship explains why an electric motor with high torque from zero rpm accelerates hard while a high-revving engine needs gearing to convert its power into usable torque at the wheels. On fasteners, applied torque is a proxy for clamping preload, and because roughly 80 to 90% of the torque is consumed by friction, lubrication significantly changes the preload achieved at a given setting.
τ = F × r × sin θ ; τ (N·m) = P (W) × 60 / (2π × rpm) ; 1 lb·ft = 1.35582 N·mSource: Newtonian rotational mechanics; SI derived unit relationships.
Worked example
A 2.4 kW motor turning at 1,450 rpm, and a wheel nut tightened by hand at 380 mm.
- Motor: ω = 2π × 1,450 / 60 = 151.8 rad/s.
- τ = 2,400 / 151.8 = 15.8 N·m.
- Wheel nut: 265 N applied at 0.38 m gives τ = 265 × 0.38 = 100.7 N·m.
The motor delivers about 15.8 N·m at rated speed; the hand-applied wheel nut torque is about 101 N·m, or 74 lb·ft.
Frequently asked questions
Does it matter whether threads are lubricated?+
Very much. Most of the applied torque overcomes friction, so an oiled thread reaches a higher clamping load at the same torque setting — often 20 to 30% more. Follow the manufacturer's condition, dry or lubricated, as specified.
How do I convert pound-feet to newton-metres?+
Multiply pound-feet by 1.35582. Note that pound-feet and foot-pounds refer to the same quantity in practice, while inch-pounds are twelve times smaller.
Why does torque fall as engine speed rises?+
Above the torque peak, breathing and friction limits mean less force per combustion cycle. Power can still climb because it multiplies torque by speed, which is why peak power occurs well after peak torque.
Can I estimate torque without a torque wrench?+
You can calculate it from force and lever length, but hand force is hard to judge and joint friction varies. For anything safety-critical — wheels, cylinder heads, structural bolts — use a calibrated wrench.
Last reviewed August 31, 2026. We review this page whenever the underlying formula, tax year, published rate or standard changes.