Rpm To Torque Calculator

Calculate motor torque from power and RPM. Enter kW, W, or HP and get instant torque in Nm, lb-ft, kgf-m, or in-lb. RPM alone cannot determine torque.

Calculate motor torque from power and rotational speed. Rotational speed alone cannot determine a twisting force, so this calculator uses both power (kW, W, or HP) and speed (RPM) to find the torque in Nm, lb-ft, kgf-m, or in-lb. It is designed for quick checks on motors, engines, rotating equipment, and drivetrains.

What This RPM to Torque Calculator Calculates

This tool calculates the theoretical torque from a known power and speed. It is a one-way calculator, meaning you provide the power and RPM, and it solves for the torque. It does not solve backward to find the power or speed from a known torque.

To function, the calculator requires both input fields to be filled with values greater than zero. Once the math is complete, the result is automatically rounded to two decimal places. You can then freely switch the output unit without needing to re-enter your initial numbers.

Tool element	What the calculator uses
Power input	kW, W, HP
Speed input	RPM
Torque output	Nm, lb-ft, kgf-m, in-lb
Minimum valid input	Greater than 0
Result formatting	Rounded to 2 decimals

RPM to Torque Formula

The calculator uses standard power-speed-torque relationships to find the result. Depending on your chosen units, it relies on specific formulas.

Metric formula$$T_{Nm} = \frac{P_{kW} \times 9549.3}{RPM}$$

Physics form used in the calculator Internally, the tool converts power to watts and applies the base physics formula before converting to your final output unit:$$T_{Nm} = \frac{P_W \times 30}{\pi \times RPM}$$

Imperial formula$$T_{lb-ft} = \frac{HP \times 5252}{RPM}$$

How to Use the RPM to Torque Calculator

1. Enter the motor power from your equipment datasheet or manual.
2. Select the power unit. Choose kW or W for most electric motors, or switch to HP if you are working with an engine or an imperial specification.
3. Enter the motor speed in RPM.
4. Read the calculated torque result.
5. Switch the torque output unit if needed. For example, if you calculate in kW but your mechanical team needs the specification in lb-ft, click the new unit to convert the result instantly.
6. Use Load Example to instantly fill the tool with a sample calculation to see how the formatting works.
7. Use Clear to reset the tool for a new calculation.

If you leave a field empty, the calculator will prompt you to enter the missing value before it runs. If you enter zero or a negative number, a validation message will appear asking for a valid input greater than zero, since a motor cannot produce power or speed at or below zero.

Example RPM to Torque Calculations

Here are common examples showing how power ratings and speeds convert into torque.

Power	Speed	Formula path	Torque
10 kW	1500 RPM	$$9549.3 \times 10 \div 1500$$	63.66 Nm
5 HP	1750 RPM	$$5252 \times 5 \div 1750$$	15.01 lb-ft
2500 W	3000 RPM	$$(2500 \times 30 / \pi) \div 3000$$	7.96 Nm

Electric motor example: 10 kW at 1500 RPM represents a standard metric electric motor. At a typical running speed, 10 kilowatts of power translates to a steady 63.66 Nm of twisting force at the shaft.

Engine/horsepower example: 5 HP at 1750 RPM shows a common industrial AC motor or small engine. Using the imperial constant, 5 horsepower at 1750 RPM delivers 15.01 lb-ft of torque.

Watts example: For smaller equipment or high-speed motors operating at 3000 RPM, 2500 watts yields a lower torque of 7.96 Nm because the energy is spread across a higher rotational speed.

RPM to Torque Conversion Table

This first table shows how a single horsepower translates into different amounts of torque depending on the motor’s speed.

Torque at 1 HP

RPM	Torque (lb-ft)	Torque (Nm)
500	10.50	14.24
1000	5.25	7.12
1500	3.50	4.75
1800	2.92	3.96
3000	1.75	2.37
5252	1.00	1.36

Because lower speeds produce more turning force for the same power, the torque drops significantly as the RPM increases. To estimate torque for another power value, simply multiply the torque row by your actual HP.

For metric equipment, this next table outlines the steady torque output of a 1-kilowatt motor across standard industrial speeds.

Torque at 1 kW

RPM	Torque (Nm)	Torque (lb-ft)
500	19.10	14.09
1000	9.55	7.05
1500	6.37	4.70
3000	3.18	2.35

You can use this as a quick reference multiplier. If you have a 10 kW motor at 1500 RPM, multiply the 6.37 Nm value by 10 to get your total torque.

Power and Torque Units Supported by This Calculator

Quantity	Units supported
Power	W, kW, HP
Speed	RPM
Torque	Nm, lb-ft, kgf-m, in-lb

• W and kW are common for electric motors.
• HP is common for engines and mixed industrial specifications.
• Nm is the standard SI torque unit.
• lb-ft is common in automotive and engine specifications.
• kgf-m and in-lb help with legacy equipment and smaller torque values.

When to Use an RPM to Torque Calculator

This tool is useful for practical mechanical and electrical sizing checks:

• Checking motor shaft torque directly from its rated power and speed to ensure it can move a specific load.
• Comparing two motors with different speed ratings to see which one provides more actual turning force at the shaft.
• Converting a datasheet power rating into a usable torque number for matching couplings or gearboxes.
• Estimating engine or machine output torque at a known power point during performance testing.
• Converting results into the specific torque unit required by your design software, maintenance sheet, or equipment catalog.

Limits of RPM to Torque Calculations

• RPM alone does not determine torque: Power is always required to calculate the twisting force.
• Theoretical vs actual: This tool calculates theoretical, steady-state torque from rated power and speed. It gives you the continuous rated torque, which is different from peak transient torque or startup/stall torque.
• Mechanical losses: The calculation does not account for drivetrain loss, gearbox reduction, or mechanical efficiency drops.
• Real-world variations: Real systems may deliver slightly different torque to the final load due to friction, heat, and varying load conditions compared to this ideal calculator output.

RPM to Torque Formula Constants Explained

• 5252 appears in HP and lb-ft calculations because 1 horsepower equals 33,000 foot-pounds per minute. Dividing 33,000 by $2\pi$ (the distance of one full rotation) gives exactly 5252.1.
• 9549.3 appears in kW and Nm calculations. It comes from dividing 60 (seconds in a minute) by $2\pi$, then multiplying by 1000 to convert watts to kilowatts.
• 9550 vs 9548.8: You might see some engineering sites use 9550 as a simplified, rounded constant, while others use 9548.8 based on slightly different gravity assumptions. This tool uses 9549.3 for standard precision.
• Rounding variations: Small output differences happen across different calculators depending on which of these rounding constants the developer chose to use in their code.

Common RPM to Torque Scenarios

Scenario	What changes	Result
RPM doubles, power stays the same	Speed increases	Torque is cut roughly in half
Power doubles, RPM stays the same	Power increases	Torque roughly doubles
Same power, lower RPM	Speed decreases	Torque increases
Same RPM, lower power	Power decreases	Torque decreases

Same power, lower RPM: If you replace a motor with a slower one that has the same power rating, the torque increases. The energy is concentrated into fewer rotations, resulting in more twisting force per turn.

Same RPM, higher power: If the speed stays constant but you install a motor with a higher kilowatt or horsepower rating, the torque increases directly in proportion to the power jump.

High-speed motors: High-speed motors often show much lower torque at the same power level because the available energy is spread across thousands of rapid rotations, reducing the force of each individual turn.

Gearbox changes: Adding a gearbox will change the final delivered torque and speed at the load, but it does not change the motor’s rated torque formula. The motor still produces the calculated torque at its shaft, which the gearbox then multiplies.

FAQs

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