CH
CalcHub

Ohm's Law Calculator

Ohm's Law is the foundation of electrical engineering. Enter any two known values — voltage, current, resistance, or power — and this calculator solves for the remaining two.

Enter Your Measurements

Results

Voltage0V
Current0A
Resistance0Ω
Power0W

How to Use This Calculator

  1. Enter any two of the four values: voltage, current, resistance, or power.
  2. Leave the other two fields empty.
  3. The calculator will solve for the missing values.

How Ohm's Law Calculation Works

Ohm's Law states that voltage equals current times resistance (V = IR). Combined with the power formula (P = VI), you can solve for any electrical quantity given two others. This calculator handles all six possible input combinations. For AC circuits with reactive loads (motors, transformers), these formulas apply to apparent power — multiply by power factor for real power.

Formula

V = I × R. P = V × I. P = I² × R. P = V² / R. Solve for unknowns from any two known values.

Frequently Asked Questions

How do I convert watts to amps?
Amps = Watts ÷ Volts. For example, a 1,200-watt appliance on a 120V circuit draws 10 amps (1200 ÷ 120 = 10).
Does Ohm's Law work for AC circuits?
For purely resistive loads (heaters, incandescent bulbs), yes. For reactive loads (motors, transformers), use impedance (Z) instead of resistance, and account for power factor.
What's the difference between watts and VA?
Watts (real power) does actual work. VA (apparent power) is voltage × current. For resistive loads they're equal. For motors and electronics, VA is higher than watts — the ratio is the power factor.

Related Calculators

Voltage Drop Calculator

Calculate voltage drop across a wire run based on distance, current, and wire gauge.

Wire Gauge Calculator

Determine the correct wire size based on amperage, distance, and voltage.

Circuit Breaker Size Calculator

Determine the correct breaker size for a circuit based on load and NEC rules.