Resistor Power Calculator

The Resistor Power Calculator finds the power dissipated by a resistor from any two of voltage, current or resistance — and suggests a safe rated power.

How to Use Resistor Power Calculator

Select a formula — P = V·I, P = I²·R or P = V²/R.
Enter the two known quantities — values support multiple unit prefixes.
Read the dissipated power — shown in W with automatic unit scaling.
Use the recommended rating — a 1.5–2× margin is suggested for reliable operation.

Formula & Theory — Resistor Power Calculator

P = V · I
P = I² · R
P = V² / R

Use Cases for Resistor Power Calculator

Power resistor selection — size shunt, snubber and bleeder resistors.
LED current limiting — verify that the limiting resistor stays within its rating.
Power supplies — check dissipation in sense resistors and inrush limiters.
Education — explore how each Ohm’s-law-derived power formula behaves.

Frequently asked questions about Resistor Power Calculator

Why add a safety factor?

Real resistors derate at higher ambient temperatures and pulse loads can briefly exceed the steady-state dissipation. A 1.5–2× margin keeps the part well within its rated lifetime.

Which formula should I use?

Use whichever two quantities you can measure most accurately. The three forms are mathematically equivalent — P = V·I always holds.

Does this account for inrush currents?

No. The calculator gives steady-state dissipation. Pulse and inrush loads require manufacturer pulse-power curves.

Is my data stored?

No. All calculations run locally in your browser; nothing is sent to any server.