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Ohm's Law Calculator

Enter any two of voltage, current, resistance, and power to solve the complete electrical circuit using Ohm's law.

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ExampleSample values — edit any field to see your result.

Results update as you type.

Resistance (R)

550Ω

Estimated result

Power (P)
22W
Voltage (V)
110V
Current (I)
0.2A
Formula
Using voltage and current: V = I × R and P = V × I.

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Resistance (R)550 Ω
Enter any two circuit values to solve voltage, current, resistance, and power. The calculator accepts common metric electrical units and converts them before solving.

How to use this calculator

Enter the known electrical quantities with the units shown beside each field. Check the solved voltage, current, resistance, and power together. These relationships describe the stated resistive model; they do not establish a component’s safe operating rating.

Examples

110 V and 0.2 A

Resistance is 110 ÷ 0.2 = 550 Ω, and power is 110 × 0.2 = 22 W.

Formula

V = I × R and P = V × I. Equivalent forms include I = V/R, R = V/I, P = I²R, and P = V²/R.
De-energize circuits before measuring resistance. Use instruments and procedures rated for the circuit voltage and fault current.

Scope and safety

The equations describe an ideal lumped circuit and do not select wire size, overcurrent protection, insulation, clearances, or component ratings. Real AC loads can also involve reactance and power factor, so resistance alone may not describe impedance. OSHA states that qualified personnel must use test equipment to verify de-energization; an indicator by itself does not establish a safe working condition. See OSHA's de-energization interpretation.

Working with AC real power

When voltage and current are known for an AC load, real power also depends on power factor. The Amps to Watts Calculator includes single-phase and balanced three-phase cases, line-to-line or line-to-neutral voltage, and a reverse watts-to-amps mode. It distinguishes real watts from apparent volt-amperes.

Frequently asked questions

What is Ohm's law?
Ohm's law states V = I × R, relating voltage in volts, current in amperes, and resistance in ohms.
How is electrical power related?
Power is P = V × I. Combining this with Ohm's law gives P = I²R and P = V²/R.
Which values should I enter?
Enter exactly two of voltage, current, resistance, and power and leave the other two blank.

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