Enter the current (amps) and up to 3 different resistances (ohms) into the calculator to determine the Total Power. 

Total Power Calculator

Enter any 4 values to calculate the missing variable

Understanding Total Power

This calculator finds the total power dissipated by up to three resistances when the same current flows through each one. That makes it especially useful for series circuits and other same-current resistive paths.

Total Power Formula

P_t = I^2R_1 + I^2R_2 + I^2R_3

If you first combine the resistances, the equation becomes even simpler:

R_t = R_1 + R_2 + R_3
P_t = I^2R_t
Symbol Meaning Typical Unit
Pt Total power dissipated by all resistances combined W
I Circuit current through each resistance A
R1, R2, R3 Individual resistance values Ω
Rt Total resistance Ω
V Total voltage across the circuit V

How to Calculate Total Power

  1. Add the resistance values to get the total resistance.
  2. Square the current value.
  3. Multiply the squared current by the total resistance.
  4. The result is the total power in watts.

Examples

If the current is 10 A and the three resistances are 50 Ω, 30 Ω, and 20 Ω:

P_t = 10^2(50 + 30 + 20) = 10000 \text{ W}

If the current is 4 A and only two resistances are used, 5 Ω and 7 Ω, the unused resistance contributes 0:

P_t = 4^2(5 + 7 + 0) = 192 \text{ W}

Quick Reference

Change Effect on Total Power
Current doubles Total power becomes 4 times larger
Current is cut in half Total power becomes 1/4 as large
All resistances double Total power doubles
Another series resistance is added Total power increases with the total resistance

If You Know Voltage Instead of Current

When total voltage is known, find current from the total resistance first, or compute power directly from voltage and total resistance:

I = \frac{V}{R_t}
P_t = \frac{V^2}{R_t}

Common Input Errors

  • Using this same-current formula for a parallel circuit without first finding branch power correctly.
  • Mixing units such as mA, A, kA, Ω, and kΩ without converting them consistently.
  • Forgetting that current is squared, which makes power rise very quickly as current increases.
  • Adding resistance values incorrectly before calculating total power.