HP to Torque Calculator: Formula and Examples

An HP-to-torque calculator converts horsepower and engine speed in revolutions per minute (RPM) into torque. Enter horsepower and RPM to get torque in pound-feet (lb-ft), with the equivalent value in newton-metres (N·m).

Formula

For horsepower in mechanical horsepower and engine speed in revolutions per minute, the formula is:

Torque (lb-ft) = Horsepower × 5,252.113 ÷ RPM

The constant comes from the relationship between power, torque, and rotational speed. In customary units, power in horsepower equals torque in lb-ft multiplied by RPM, divided by approximately 5,252.113. Rearranging that relationship gives the calculator formula.

• Horsepower (hp): mechanical horsepower, a measure of power.
• RPM: revolutions per minute, the rotational speed at which the horsepower applies.
• Torque (lb-ft): rotational force expressed in pound-feet.
• Torque (N·m): the same quantity converted to newton-metres; 1 lb-ft equals 1.355817948 N·m.

RPM must be greater than zero because division by zero is undefined. The calculator accepts nonnegative horsepower, so zero horsepower returns zero torque. Its input units matter: use horsepower and RPM, not kilowatts or revolutions per second, unless you convert them first.

Worked Example

Using the calculator’s default values, horsepower is 100 hp and engine speed is 3,000 RPM.

1. Multiply horsepower by the constant: 100 × 5,252.113122 = 525,211.3122.
2. Divide by engine speed: 525,211.3122 ÷ 3,000 = 175.0704374 lb-ft.
3. Round to two decimal places: 175.07 lb-ft.
4. Convert to metric: 175.0704374 × 1.355817948 = 237.366… N·m, or 237.37 N·m.

When to Use an HP-to-Torque Calculator

This conversion is useful when a specification gives horsepower and RPM but you want to compare torque at that same engine speed. It can help interpret a dynamometer chart, check a published engine figure, or understand how power and torque relate in a vehicle or machine. The result is a value at the RPM entered—not a complete description of the engine’s performance.

For example, 100 hp at 3,000 RPM corresponds to about 175.07 lb-ft. If the same 100 hp occurs at 6,000 RPM, calculated torque is about 87.54 lb-ft. The power is unchanged, but it is being delivered at twice the rotational speed, so torque is half as large.

That does not mean the higher-revving engine is necessarily less capable. Gearing can trade rotational speed for torque at the wheels, while losses in a drivetrain affect the power that reaches them. To compare vehicle performance, consider the full torque curve, gearing, vehicle mass, traction, and the conditions of the measurement—not one converted number alone.

How Horsepower and Torque Relate

Torque describes a turning effect; horsepower describes how quickly work is done. In a rotating system, power depends on both torque and rotational speed. Consequently, the torque associated with a given horsepower falls as RPM rises, and rises as RPM falls, provided horsepower remains constant.

In US customary usage, the familiar relation is horsepower = torque in lb-ft × RPM ÷ 5,252.113. The number 5,252 is often rounded in automotive explanations. It is a unit-conversion constant, not a special engine speed at which every engine makes equal horsepower and torque. The frequently noticed crossing of horsepower and torque curves near 5,252 RPM applies only when torque is shown in lb-ft and horsepower on the same graph with matching numerical scales. It is not a universal feature of an engine.

Metric power ratings require attention to the unit. A kilowatt is not a horsepower: 1 mechanical hp is approximately 0.7457 kW. If power is supplied in kilowatts, convert it to mechanical horsepower before using this calculator, or use a consistent metric equation: torque in N·m = power in kW × 9,549.3 ÷ RPM. Do not substitute a metric horsepower value for mechanical horsepower without checking which definition the specification uses.

Reading Results and Avoiding Mistakes

• Match the RPM to the power figure. Horsepower and RPM must describe the same operating point. Combining peak horsepower from one speed with RPM from another does not reveal the engine’s actual torque at either point.
• Check the horsepower definition. Mechanical horsepower, metric horsepower, and electrical horsepower can differ slightly. This calculator assumes mechanical horsepower.
• Keep speed in RPM. The constant 5,252.113 assumes revolutions per minute. If speed is given in revolutions per second, multiply it by 60 before using the formula.
• Keep torque units distinct. A pound-foot (lb-ft) and a pound-inch (lb-in) are not interchangeable; 1 lb-ft equals 12 lb-in. The metric output is N·m, not N·cm.
• Do not overread precision. The calculator rounds displayed results to two decimals, but the input figures may themselves be rounded or measured with uncertainty. Extra decimal places would not make an approximate source value exact.

What the Calculation Cannot Tell You

The conversion does not estimate horsepower from torque alone: RPM is also required. Nor does one point tell you peak torque, peak horsepower, fuel use, acceleration, or how the engine behaves across its operating range. For those questions, you need suitable measurements or a power-and-torque curve.

Test conditions also matter. An engine-dynamometer reading and a wheel-dynamometer reading may differ because one measures output at the engine and the other includes drivetrain effects. Corrections, equipment, temperature, and test procedure can affect reported figures. Treat the calculator as a unit-and-relationship tool, not as a substitute for a properly identified measurement.

Frequently Asked Questions

How do I calculate torque from horsepower and RPM?
Multiply horsepower by 5,252.113, then divide by RPM to get lb-ft. Convert lb-ft to N·m by multiplying by 1.355817948.

How much torque is 1 hp?
There is no single torque value for 1 hp; it depends on RPM. At 1,000 RPM, 1 hp corresponds to about 5.25 lb-ft. At 2,000 RPM, it corresponds to about 2.63 lb-ft.

Can I calculate horsepower from torque?
Yes, if you also know RPM: horsepower = torque in lb-ft × RPM ÷ 5,252.113. Torque by itself is not enough to determine horsepower.

Why does torque decrease when RPM increases?
That is true when horsepower is held constant. Since power depends on torque multiplied by rotational speed, maintaining the same power at a higher RPM requires less torque. Real engines do not necessarily maintain constant horsepower across their RPM range.

Does this calculator use wheel torque?
No. It converts the horsepower and RPM values you enter without identifying where they were measured. If the horsepower is measured at the wheels, the result corresponds to that input figure; the calculator does not add or remove drivetrain losses.

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in hp | Horsepower | hp | 100 | 0
in rpm | Engine speed | rpm | 3000 | 0.000001
out torque | Torque | lb-ft | hp * 5252.113122 / rpm | 2
out nm | Torque | N·m | torque * 1.355817948 | 2