HP to Torque Nm Calculator: Convert Power and RPM

Convert horsepower (hp) and engine speed (rpm) into torque in newton-metres (Nm) with this calculator. Enter power and rpm; the result is the torque implied at that rotational speed, with an optional equivalent in pound-feet.

Formula

Torque is power divided by angular speed. In SI units, the relationship is T = P / ω, where T is torque in newton-metres (Nm), P is power in watts (W), and ω is angular speed in radians per second (rad/s). Since one mechanical horsepower is 745.699871582 watts and rpm converts to radians per second by multiplying by 2π/60, the calculator uses:

Torque (Nm) = hp × 745.699871582 ÷ (2π × rpm ÷ 60)

• hp is mechanical horsepower.
• rpm is rotational speed in revolutions per minute.
• π is approximately 3.14159.
• Nm is the SI unit of torque; the additional output converts it to pound-feet (lb-ft).

The reverse relationship is useful too: hp = torque in Nm × rpm ÷ 7127. 7127 is a rounded conversion constant for this particular combination of mechanical horsepower, Nm, and rpm.

Worked Example

Using the calculator’s defaults—100 hp at 3,000 rpm:

1. Convert power: 100 × 745.699871582 = 74,569.9871582 W.
2. Convert speed: 2π × 3,000 ÷ 60 = 314.159265 rad/s.
3. Divide power by angular speed: 74,569.9871582 ÷ 314.159265 = 237.56 Nm, rounded to two decimal places.
4. Convert to pound-feet: 237.56 ÷ 1.3558179483314 = 175.21 lb-ft, rounded to two decimal places.

So 100 mechanical hp at 3,000 rpm corresponds to approximately 237.56 Nm (175.21 lb-ft) at that speed.

When to Use an HP-to-Torque Calculator

Power and torque describe related but different aspects of rotational output. Torque is the turning effect available at a particular shaft speed. Power describes how quickly work is done. The conversion is handy when a specification gives horsepower and rpm but you want to compare torque at that same rpm, or when checking a power-and-torque figure for consistency.

The rpm value matters: horsepower alone cannot determine torque. The same power corresponds to more torque at lower rpm and less torque at higher rpm. For example, this calculator’s 100 hp corresponds to about 475.11 Nm at 1,500 rpm, but about 118.78 Nm at 6,000 rpm. These are mathematical values at the stated speeds, not a claim that a particular engine produces 100 hp at either speed.

How to Interpret the Result

Read the answer as torque at the exact rotational speed entered. It is not necessarily the engine’s peak torque, its maximum torque, or the torque available throughout its rev range. To find torque at several speeds, calculate each speed separately using the power available at that speed. In a real engine, power generally changes with rpm, so using one horsepower figure across an entire speed range can give misleading results.

Torque also does not directly tell you how quickly a vehicle accelerates. Vehicle mass, gearing, tire size, traction, losses in the drivetrain, and the shape of the engine’s power curve all affect what reaches the wheels and how the vehicle responds. A transmission can multiply torque at the wheels while reducing their rotational speed; it does not create power, and real systems have losses.

Units, Horsepower Types, and Common Mistakes

This calculator treats hp as mechanical horsepower, defined as approximately 745.7 W. Metric horsepower, often written PS or CV, is approximately 735.5 W. If a source uses metric horsepower, convert it to mechanical hp first: multiply PS by about 0.98632, then enter that result. Do not assume that every source’s “hp” label uses the same definition.

• Mixing torque units: 1 Nm is approximately 0.73756 lb-ft, and 1 lb-ft is approximately 1.35582 Nm. A newton-metre is not the same size as a pound-foot.
• Confusing lb-ft with ft-lb: Both labels are commonly used for the same torque unit, though technical writing often prefers lb-ft. They are not pound-force per square foot.
• Using the wrong speed: Enter rpm, not revolutions per second. If speed is given in revolutions per second, multiply by 60 first.
• Rounding too early: Keep full precision during the calculation and round the final result. Displayed values are rounded, so reverse calculations may differ slightly.
• Assuming peak figures occur together: Maximum horsepower and maximum torque often occur at different rpm. A peak horsepower number cannot be paired with peak torque unless both are specified at the same speed.

Limits and Related Comparisons

The formula is a direct conversion based on power and rotational speed; it does not measure an engine. Its answer is meaningful only when the entered horsepower applies at the entered rpm and both values refer to the same point in the system. For example, an engine’s crankshaft output and a wheel-dynamometer result are not interchangeable because drivetrain losses separate them.

Power figures can also depend on how they were measured or reported. A bare horsepower value without a measurement standard, correction method, or rpm may be insufficient for a precise comparison. Use the definitions and conditions supplied with the specification, and treat calculator outputs as arithmetic rather than independently verified performance data.

Frequently Asked Questions

How many Nm is 1 hp?
There is no single Nm equivalent for 1 hp without an rpm value. Torque depends on speed: at 1,000 rpm, 1 mechanical hp corresponds to about 7.12 Nm; at 3,000 rpm, it is about 2.38 Nm.

What is the formula for hp to Nm?
For mechanical horsepower and rpm, Nm = hp × 7127 ÷ rpm, approximately. The calculator uses the underlying unit conversions rather than relying on the rounded constant.

Can I calculate torque from horsepower alone?
No. You also need rotational speed. At a given horsepower, torque changes inversely with rpm.

Is hp the same as PS?
No. Mechanical horsepower is about 745.7 W, while metric horsepower (PS) is about 735.5 W. Convert the units before comparing values precisely.

Why does a vehicle’s torque figure differ from this result?
The figures may refer to different rpm, different measurement points, different horsepower definitions, or different test conditions. The calculator only converts power and speed that apply together at the same point.

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in hp | Power | hp | 100 | 0
in rpm | Engine speed | rpm | 3000 | 0
out torque | Torque | Nm | hp * 745.699871582 / (2 * pi * rpm / 60) | 2
out lbft | Torque | lb-ft | torque / 1.3558179483314 | 2