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Ohms Law Calculator

Enter any two of voltage, current, resistance and power, and find the other two.

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ItemValue
Enter exactly two values and leave the others blank. This is for learning and planning. Mains electrical work can be dangerous, so use a qualified electrician.

Quick Answer

Ohm’s law says voltage equals current times resistance: V = I × R. Power is P = V × I. For example, 12 V at 2 A means a resistance of 6 Ω and a power of 24 W.

Last updated: 2 November 2026 · How we calculate this: Ohm’s law and the power formula

Table of Contents

How This Ohms Law Calculator Works

Ohm’s law links voltage, current and resistance. Add the power formula, and any two values give you the other two. Enter two values, leave the others blank, and press Calculate.

Quick explanation: V = I × R, and P = V × I.

  • Voltage (V): electrical pressure, in volts.
  • Current (I): flow of charge, in amps.
  • Resistance (R): opposition to flow, in ohms.
  • Power (P): rate of energy use, in watts.

Core Formulas

  • Voltage: V = I × R, or V = P ÷ I, or V = √(P × R)
  • Current: I = V ÷ R, or I = P ÷ V, or I = √(P ÷ R)
  • Resistance: R = V ÷ I, or R = V² ÷ P, or R = P ÷ I²
  • Power: P = V × I, or P = I² × R, or P = V² ÷ R

Worked Example

A 60 W device runs on 120 V.

  • Current = 60 ÷ 120 = 0.5 A
  • Resistance = 120 ÷ 0.5 = 240 Ω

Things to Keep in Mind

  • DC and simple AC loads: these formulas suit basic resistive loads.
  • Motors and electronics: AC loads may need power factor, which is not included here.
  • Safety: do not rely on this calculator for wiring or breaker sizing.

Frequently Asked Questions

It says voltage equals current times resistance: V = I × R.

Divide voltage by resistance. For example, 12 V ÷ 6 Ω = 2 A.

Multiply volts by amps. For example, 120 V × 2 A = 240 W.

Two. The calculator finds the other two values.

No. It suits resistive parts best. Diodes, for example, do not follow it in a simple way.

References & Sources

SourceUsed ForLink
Wikipedia, Ohm’s law The relation between voltage, current and resistance. https://en.wikipedia.org/wiki/Ohm%27s_law
Wikipedia, Electric power Power formulas. https://en.wikipedia.org/wiki/Electric_power