The Horsepower Formula
A common rule of thumb for imperial units (lb-ft and RPM):
HP = (Torque × RPM) / 5252
This constant (5252) comes from converting units to match the definition of 1 HP (33,000 ft-lb/min).
Rotational Power Calculator
Calculate rotational power, torque, or angular velocity including RPM and horsepower conversions.
Rotational Power
Calculate engine Horsepower, Torque, or RPM instantly.
P = τ · ω
Engines & Motors
Rotational power is essential for understanding how engines deliver energy to wheels or how electric motors drive machinery.
SI Formula (Metric)
When using standard metric units (N·m and rad/s), the formula is clean:
Watts = N·m × rad/s
No extra constants required! This is why physics prefers radians.
rotational power formulas and interpretation
Rotational power is the rate at which torque transfers mechanical energy at a given rotation speed.
The calculator preserves direct solutions for power, torque, and rotational speed.
How to use the rotational power calculator
- Choose a model: Select the physical relationship that matches the known values.
- Choose the unknown: Select the quantity you need to calculate.
- Enter values and units: Provide every requested measurement using consistent units.
- Calculate: Check the formula, converted result, sign, and units.
Formula and variables
Rotational power equals torque multiplied by angular velocity in radians per second.
P = τω- P — Power
- Mechanical energy transfer rate (W)
- τ — Torque
- Turning moment (N·m)
- ω — Angular velocity
- Rotation rate (rad/s)
Motor power example
A motor produces 50 N·m at 100 rad/s.
- Torque
- 50 N·m
- Angular velocity
- 100 rad/s
- P = 50 × 100
- P = 5,000 W
Result: Rotational power is 5 kW.
The shaft transfers mechanical energy at 5,000 joules per second.
Understanding your results
Interpreting the result
At fixed torque, power rises in direct proportion to rotational speed.
A sign indicates direction only when a consistent rotational sign convention is used.
Assumptions
- Rotation is evaluated about a specified axis.
- Inputs are converted through coherent SI units.
- The selected formula adequately represents the physical system.
Limitations
- The calculator does not simulate time-varying inputs.
- Vector directions and multiple axes must be resolved separately.
- Losses such as friction are not added unless represented in the entered net value.
Common mistakes
- Mixing RPM with radians per second.
- Using diameter instead of radius.
- Entering a zero divisor.
- Ignoring the direction represented by a negative value.
Practical use cases
Physics and education
Check rotational kinematics and dynamics exercises.
Machines and mechanisms
Estimate quantities for wheels, shafts, rotors, and rotating equipment.
Frequently asked questions
Why are radians used in rotational formulas?
Radians make angular and linear relationships dimensionally coherent without an extra conversion factor.
Can the result be negative?
Yes. A negative value means the quantity points opposite the direction chosen as positive.
Sources and review
- SI Brochure, 9th edition — BIPM. Accessed 2026-07-11.
- Special Publication 811 — NIST. Accessed 2026-07-11.
Reviewed 2026-07-11.
Related Calculators
Continue with calculators that answer nearby questions and help compare the next step.
Rotational Dynamics Calculator
Use this free rotational dynamics for science calculations. Get instant, accurate results with clear inputs and no signup required.
Torque Calculator
Use this free torque calculator for science calculations. Get instant, accurate results with clear inputs and no signup required.
Power Calculator
Calculate work-time, force-velocity, and voltage-current power relationships with unit conversion.
Work Energy Calculator
Use this free work energy for science calculations. Get instant, accurate results with clear inputs and no signup required.