Fundamentals calculator

Ohm's Law & Power Calculator

Enter any two of voltage, current, resistance and power; the other two are calculated instantly.

BasicsBasis: Ohm’s law · Joule’s law

Inputs

V
A
Ω
W

Results

Enter values to calculate
—

Formula

V = I · R   P = V · I = I² · R = V² / R

Worked example

12 V across a load drawing 2 A: R = 12 / 2 = 6 Ω, P = 12 × 2 = 24 W.

Assumptions and standards

  • DC or purely resistive AC (RMS values). For reactive AC loads use impedance and power factor instead.
  • Fill exactly two fields; leave the other two blank.

Formula and data last verified: October 2026.

Frequently asked questions

Does Ohm’s law apply to AC?

Yes, with impedance Z in place of R and RMS values. For capacitors, inductors and motors, real power also depends on the power factor.

Can I use these results for final design?

Use them for preliminary design and checking. Final designs must be verified by a qualified engineer against the code edition and standards adopted where the work is installed.

Is my data sent anywhere?

No. Every calculation runs in your browser. Nothing you type is uploaded or stored on our servers.

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