Calculate voltage from torque, current, and speed, or find RPM from voltage with selectable units for RPM, RPS, Hz, V, mV, and kV.

RPM to Voltage Calculator

Enter torque and current, then enter either speed or voltage (leave the other blank) to calculate it.

N·m
A

Note: “Hz” is treated as revolutions per second (same as RPS).

Voltage from RPM Formula

The following formula is used to calculate the Voltage from RPM (rotational speed), torque, and current using an ideal power-balance assumption.

V = (2π) / (60) × (t × w) / (I)
  • Where V is the Voltage from RPM (volts)
  • t is the torque (N·m) 
  • w is the rotational speed (RPM) 
  • I is the current (amps) 

To calculate the voltage from RPM, multiply the torque by the RPM, divide by the current, then multiply by 2 times pi over 60 (which converts RPM to radians per second).

Important: This relationship comes from equating mechanical power Pmech = τ·ω to electrical power Pelec = V·I, which assumes ideal (100% efficient) conversion and DC electrical power. It does not represent a motor’s back-EMF/open-circuit generator voltage in general (those depend on machine constants, losses, and for AC, power factor and phase).

Example RPM to Voltage Conversion Table (t = 15 N·m, I = 50 A)
RPM Voltage (V)
10.0314
50.1571
100.3142
300.9425
601.8850
1003.1416
2006.2832
3009.4248
50015.7080
60018.8496
75023.5619
100031.4159
120037.6991
150047.1239
180056.5487
200062.8319
250078.5398
300094.2478
3600113.0973
5000157.0796
* Calculated using V = (2π/60) × t × RPM ÷ I with fixed example values t = 15 N·m and I = 50 A (so V ≈ 0.0314159 × RPM).

How to Calculate Voltage from RPM?

The following example problems outline how to calculate Voltage from RPM.

Example Problem #1

  1. First, determine the torque (N-m). In this example, the torque (N-m) is determined to be 15 .
  2. Next, determine the RPM. For this problem, the RPM is measured to be 4 .
  3. Next, determine the current (amps). In this case, the current (amps) is found to be 50.
  4. Finally, calculate the Voltage from RPM using the formula above: 

V = 2π / 60 * t * w / I

Inserting the values from above and solving yields: 

V = 2*3.14159/ 60 * 15 * 4 / 50 = .125 (volts)

Example Problem #2

Using the same method as above, determine the variables required by the formula. For this example problem, these are:

torque (N-m) = 41

RPM = 1

current (amps) = 52

Enter these given values into the calculator above yields: 

V = 2*3.1415/ 60 * 41 * 1 / 52 = .082 (volts)