Which formula should I use?

Use R = V² / P when you know the voltage across the load and its power rating. Use R = P / I² when you know the current through it and its power rating.

What units does this calculator expect?

Power in watts (W), voltage in volts (V), and current in amperes (A). The result is in ohms (Ω).

Can I enter milliwatts or milliamps?

Convert to base units first: divide milliwatts by 1000 to get watts, and milliamps by 1000 to get amps.

Does this work for AC circuits?

For purely resistive AC loads the formulas are identical. For reactive loads (inductors, capacitors) the result is impedance magnitude, not pure resistance.

Why does the result change so much with small input changes?

Resistance is proportional to V² / P, so doubling voltage quadruples resistance at the same power. This sensitivity is normal and expected from the formula.

How many ohms is 60 watts?

It depends on the voltage or current. At 120 V, R = V²/P = 120²/60 = 240 Ω. At 12 V, R = 144/60 = 2.4 Ω. Enter your actual voltage or current to get the exact resistance.

Watts to Ohms Calculator

Name: Watts to Ohms Calculator
Availability: InStock
Author: Nham Vu

Convert watts to ohms using R = V²/P (voltage + power) or R = P/I² (power + current) — two solve modes.

Enter Values

Solve mode

R = V² / P — enter power and voltage

Power (W) *

Voltage (V) *

Select a mode, enter the values, and click Calculate.

Resistance

0 Ω

Formula Applied

Parameter	Value

Copied!

Summary

Convert watts to ohms using R = V²/P (voltage + power) or R = P/I² (power + current) — two solve modes.

How it works

Select the solve mode: V² / P (voltage + power) or P / I² (power + current).
Enter the power in watts.
Enter either the voltage in volts (Mode 1) or current in amps (Mode 2).
Click Calculate to compute resistance in ohms.
The result panel shows the formula applied, derived quantities, and a copy button.

Use cases

Find the resistance of a heating element from its wattage rating and supply voltage.
Determine wire or fuse resistance from measured power dissipation and current draw.
Verify that a resistor's value matches a circuit's power and voltage spec.
Size protective resistors by knowing load power and current limits.
Cross-check circuit designs by comparing calculated and measured resistance.
Quickly estimate speaker or motor winding impedance from rated watts and voltage.

Frequently Asked Questions

Last updated: 2026-06-14 · Reviewed by Nham Vu