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Ohm's Law

Free Ohm's Law calculator with clear step-by-step results.

About Ohm's Law

Solves Ohm's law for whichever of voltage, current or resistance you are missing, then derives power from the two known quantities. Division is guarded so a zero resistance or zero current returns zero rather than an infinite result.

Formulas

Ohm's law

V = I x R, so I = V / R and R = V / I

Power

P = V x I, equivalently I^2 x R or V^2 / R

Worked example

With the default values below, Ohm's Law returns Power dissipated of 6.0000. Change any input above and every figure here is recalculated in your browser.

Inputs used

Quantity to solve forone of Current (I), Voltage (V), Resistance (R)
Current (I)
Voltageminimum 0 V
12 V
Currentminimum 0 A
0.5 A
Resistanceminimum 0 ohm
24 ohm

Results

Power dissipated
6.0000 W
Voltage
12.0000 V
Current
0.5000 A
Resistance
24.0000 ohm

Step by step

  1. 1Values used
  2. 2Ohm's law
  3. 3Power
  4. 4Power dissipated= 6.0000 W
  5. 5Voltage= 12.0000 V
  6. 6Current= 0.5000 A
  7. 7Resistance= 24.0000 ohm

Assumptions and limits

  • The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 4 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
  • Mains voltages are lethal. Calculations here are for understanding circuit relationships only, not a substitute for proper electrical design, protection and qualified installation.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Mains voltages are lethal. Calculations here are for understanding circuit relationships only, not a substitute for proper electrical design, protection and qualified installation.

Frequently Asked Questions

Does Ohm's law apply to everything?

Only to ohmic components whose resistance is constant. Diodes, LEDs, incandescent filaments and semiconductors are non-linear, so their resistance changes with the operating point.

Why does the power figure matter?

It determines the resistor wattage rating you need. A resistor dissipating 0.5 W in a 0.25 W package will overheat and drift or fail.

Related Calculators

Ohm's Law – Calculate Power dissipated & Voltage | Calcrivo