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Electrical Calculators

Resistor Power Calculator

Verified formula Updated Jun 2026 Private — runs on your device

Enter details
V
Ω
Verified formula Private

Power dissipated

1.4400

Current
0.1200

For general information only — not financial, tax, legal or medical advice. Verify before you rely on it.

How to use the Resistor Power Calculator

The Resistor Power Calculator works out your power dissipated, along with 1 related figure in an instant. Enter voltage across resistor and resistance and the result updates as you type — it is free, needs no sign-up, and runs entirely in your browser so your figures stay private.

  1. Enter the voltage across resistor.
  2. Enter the resistance.
  3. Read off your power dissipated, together with current — the calculator updates automatically, with no button to press.

Formula

The Resistor Power Calculator uses the formula:

Power dissipated = Voltage across resistor ^ 2 ÷ Resistance

Worked example

For example, with voltage across resistor of 12 V and resistance of 100 Ω, the power dissipated is 1.4400.

Inputs used
Voltage across resistor 12 V
Resistance 100 Ω
Results
Power dissipated 1.4400
Current 0.1200

Results are estimates for educational use, not professional advice.

Frequently asked questions

Use P = V² ÷ R. With 12 V across a 100 ohm resistor, the power is 144 ÷ 100 = 1.44 watts.

A resistor that dissipates more power than its rating overheats and fails. Always choose a rating above the calculated power.

A common rule is to use a resistor rated at least twice the calculated power, giving headroom for heat and reliability.

Yes. Power also equals I² × R or V × I. This tool uses the voltage and resistance you enter.

Enter the voltage across resistor. Enter the resistance. Read off your power dissipated, together with current — the calculator updates automatically, with no button to press.

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