What This Calculator Does
This tool converts engine power (horsepower) and rotational speed (RPM) into torque, measured in pound-feet (lb-ft) and newton-metres (N·m). Power and torque are related by engine speed, so knowing any two lets you solve for the third. This calculator solves for torque given horsepower and RPM.
How to Use It
Enter the engine's horsepower (HP) and the engine speed (RPM) at which that power figure is produced — typically the RPM stated on a dyno sheet or spec table. The calculator instantly returns torque in lb-ft and the metric equivalent in N·m.
The Formula Explained
The relationship is $$\text{Torque (lb-ft)} = \frac{\text{HP} \times 5252}{\text{RPM}}$$ The constant 5252 comes from the definition of horsepower: 1 HP = 33,000 ft-lb per minute, and dividing 33,000 by \(2\pi\) gives roughly 5252. This is why horsepower and torque curves always cross at exactly 5252 RPM on a dyno chart.
Worked Example
An engine produces 300 HP at 6,000 RPM. $$\text{Torque} = \frac{300 \times 5252}{6000} = \frac{1{,}575{,}600}{6000} = 262.6 \text{ lb-ft}$$ Converting to metric: \(262.6 \times 1.355818 \approx 356.0\) N·m.
FAQ
Why is 5252 the magic number? It is a unit-conversion constant linking horsepower (work per minute) to torque (rotational force), derived from \(33{,}000 \div 2\pi\).
Does this work for any engine? Yes — the formula is universal for any rotating machine where you know power and speed.
Can I go from torque to horsepower? Rearrange it: $$\text{HP} = \frac{\text{Torque} \times \text{RPM}}{5252}$$
