Ohm's Law Calculator

Solve for voltage, current, resistance or power from any two known values.

By CalcHub Editorial · Last reviewed

Quick answer

  • Formula: V = I × R; P = V × I (also I = V ÷ R, R = V ÷ I)
  • Worked example — Voltage: 20.0000 V (full example below).

Ohm's Law Calculator

Voltage mode: current in amps. Current mode: voltage in volts. Resistance/power modes: voltage in volts.
Voltage mode: resistance in ohms. Current mode: resistance in ohms. Resistance/power modes: current in amps.
Worked example result
Voltage20.0000 V
Current2.0000 A
Resistance10.0000 Ω
Power40.0000 W

A current of 2 A through a 10 Ω resistor needs 20 V and dissipates 40 W.

Ohm's law links voltage, current and resistance in a circuit: V = I × R. Combined with the power relation P = V × I, any two known quantities determine the other two.

Choose what you want to find, then enter the two known values. For voltage you need current and resistance; for current, voltage and resistance; for resistance or power, voltage and current. All four results are shown together.

The formula

V = I × R; P = V × I (also I = V ÷ R, R = V ÷ I)

Worked example

A current of 2 A through a 10 Ω resistor needs 20 V and dissipates 40 W.

The example is pre-loaded in the result panel — press Calculate with your own numbers to replace it.

Frequently asked questions

What are the four Ohm's law formulas?

V = I × R, I = V ÷ R, R = V ÷ I and P = V × I. Power can also be written as P = I² × R or P = V² ÷ R — all are equivalent.

Does Ohm's law apply to every component?

It applies exactly to ohmic (resistive) components at constant temperature. Diodes, transistors and heating filaments are non-ohmic, so their V–I relationship is not a single fixed resistance.

Category: Science calculators

Sources & methodology

This calculator applies the formula shown on this page exactly as written, using the standard definitions for its inputs. Results are computed from the values you enter — no data is stored — and are rounded only for display.

Content last reviewed by CalcHub Editorial.

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