Engine Torque Calculator

Categories: Tools & Calculator

Calculate engine torque in lb-ft and N-m using horsepower (HP) or kilowatts (kW) and RPM. View step-by-step equations and our quick-reference engine speed table.

Engine Torque Calculator

HP
RPM
Please enter valid positive numbers for Power and RPM.

Calculated Rotational Torque

0
Pound-Feet (lb-ft)
0
Newton-Meters (N-m)

The Engine Torque Formula

Engine torque represents the rotational twisting force produced at the crankshaft. It is mathematically related to the engine's power output (horsepower or kilowatts) and its rotational speed (RPM).

Depending on whether you start with Imperial units (horsepower) or Metric units (kilowatts), the formulas to isolate torque are defined as follows:

1. Calculating Torque from Horsepower (Imperial)

When starting with horsepower, torque is measured in pound-feet (lb-ft):

Torque (lb-ft) = (Power in HP × 5,252) ÷ RPM

To convert the resulting pound-feet into metric Newton-meters (N-m), multiply the result by 1.355818.

2. Calculating Torque from Kilowatts (Metric)

When starting with kilowatts, torque is measured in Newton-meters (N-m):

Torque (N-m) = (Power in kW × 9,549) ÷ RPM

To convert Newton-meters back to pound-feet, multiply the result by 0.737562.

Torque vs. Engine Speed Reference Table

Because horsepower is the product of torque and RPM, a given power output requires more torque at lower engine speeds and less torque at higher engine speeds. The table below illustrates this relationship by displaying the torque required to maintain a constant 300 HP at various RPM points:

Engine Speed (RPM)Target PowerRequired Torque (lb-ft)Required Torque (N-m)
2,000 RPM300 HP788 lb-ft1,068 N-m
3,000 RPM300 HP525 lb-ft712 N-m
4,000 RPM300 HP394 lb-ft534 N-m
5,000 RPM300 HP315 lb-ft427 N-m
6,000 RPM300 HP263 lb-ft356 N-m
7,000 RPM300 HP225 lb-ft305 N-m
8,000 RPM300 HP197 lb-ft267 N-m

Contextual Information: The Physics of Torque

Torque is the physical quantity representing the capacity to rotate an object. In automotive engineering, it is the underlying force that dictates a vehicle's initial acceleration and pulling ability.

How Torque Interacts with RPM

An engine cannot produce peak power at very low RPM because it is not performing work fast enough, even if its rotational force (torque) is high. As RPM rises, the rate of work increases. This is why engines with relatively low peak torque—such as motorcycle or Formula 1 engines—can generate exceptionally high horsepower by spinning to 10,000 RPM or higher.

Why Engine Types Have Different Torque Profiles

Different combustion designs yield highly diverse torque characteristics: