Electronics Tools

LED Resistor Calculator

Choose a current limiting resistor for a single LED. Enter the supply voltage, forward voltage, and target LED current to estimate resistance, heat, and a practical standard resistor value.

What this tool doesFinds the resistor that sets LED current in a simple series circuit.

Use a higher standard valueWhen choosing from a parts bin, round up to reduce current rather than down.

Power mattersCheck resistor heat, especially with 12 V supplies or higher LED current.

Calculator

Supply voltage

LED forward voltage

Forward voltage, Vf

Target current, mA

Standard resistor series

Resistor power rating

Results

Calculated resistor

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Recommended standard value

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Resistor power

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Formula

The resistor drops the voltage left over after the LED forward voltage. Current must be in amps when using Ohm’s law.

R = (Vs – Vf) / I P = I^2 x R

Practical Notes

LED forward voltage is an estimate. Check the datasheet when brightness or battery life matters.
For indicator LEDs, 2 mA to 10 mA is often enough with modern high-efficiency parts.
This calculator is for one LED in series with one resistor. Parallel LEDs need separate current balancing.