Calculate torque from RPM and power in hp or kW, or work in reverse to find RPM or power from torque, with results in N·m and lbf·ft.
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Torque From RPM Formula
Torque requires both shaft power and rotational speed; RPM alone is insufficient. The following form uses mechanical horsepower and positive RPM.
- Where T is the Torque From RPM (lb-ft)
- P is mechanical shaft power (hp).
- S is the rotational speed (RPM)
For mechanical hp and torque in lbf·ft, multiply hp by 33,000/(2π) ≈ 5252.113122 and divide by positive RPM. In SI units, torque in N·m = power in watts divided by angular speed in rad/s. The calculator retains full π.
| Rotational Speed (RPM) | Torque (lb-ft) |
|---|---|
| 500 | 10.504 |
| 750 | 7.003 |
| 1,000 | 5.252 |
| 1,200 | 4.377 |
| 1,500 | 3.501 |
| 1,800 | 2.918 |
| 2,000 | 2.626 |
| 2,500 | 2.101 |
| 3,000 | 1.751 |
| 3,600 | 1.459 |
| 4,000 | 1.313 |
| 4,500 | 1.167 |
| 5,000 | 1.050 |
| 5,252 | 1.000 |
| 5,500 | 0.955 |
| 6,000 | 0.875 |
| 6,500 | 0.808 |
| 7,000 | 0.750 |
| 7,500 | 0.700 |
| 8,000 | 0.657 |
| * Rounded to 3 decimals. Assumes constant power of 1 HP. To scale for other power levels, multiply torque values by your HP. 1 lbf·ft = 1.3558179483314004 N·m. These algebraic operating points do not imply that a machine can deliver constant power across its full speed range. | |
How to Calculate Torque From RPM?
The following two example problems outline how to calculate the Torque From RPM.
Example Problem #1:
- First, determine the total power (HP). In this example, the total power (HP) is measured to be 500.
- Next, determine the rotational speed (RPM). For this problem, the rotational speed (RPM) is calculated to be 1000.
- Finally, calculate the Torque From RPM using the formula above:
T = (33000 / (2*pi)) * P / S
Inserting the values from above and solving the equation with the imputed values gives:
T = 33000 × 500 / (2π × 1000) ≈ 2626.06 lbf·ft
Example Problem #2:
Using the same process as example problem 1, we first define the variables outlined by the formula. In this case, the values are:
total power (HP) = 600
rotational speed (RPM) = 2000
Entering these values into the formula or calculator above gives us
T = 33000 × 600 / (2π × 2000) ≈ 1575.63 lbf·ft
