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Resistance Calculator

Calculate electrical resistance from voltage and current using Ohm’s law, plus power.

V
A
Resistance
6 Ω
R = 12 V ÷ 2 A = 6 Ω (Ohm’s law)
Power
24 W
Voltage
12 V
Current
2 A

Results are theoretical — real-world resistance varies with temperature, wire gauge, and component tolerances. Verify against component datasheets and local electrical codes.

How it works

  1. 1Enter the voltage (V) across the component.
  2. 2Enter the current (A) flowing through it.
  3. 3The calculator applies R = V ÷ I and shows the power in watts.

Use cases

  • Sizing resistors in LED or motor-driver circuits.
  • Verifying that measured voltage and current match a rated resistance.
  • Finding power dissipation when designing enclosures or heat sinks.

Frequently asked questions

What is the formula for resistance?

Resistance R = V ÷ I (Ohm’s law). For example, 12 V across a component drawing 2 A gives 6 Ω.

How does resistance combine in series and parallel?

In series, resistances add: R = R₁ + R₂. In parallel, 1/R = 1/R₁ + 1/R₂, giving a total lower than the smallest resistor.

Why does it show — when current is zero?

With no current, Ohm’s law cannot determine resistance from voltage alone (division by zero). Enter a non-zero current to get a result.

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