💡 Electronics

LED Series Resistor Calculator

Calculate the resistor, current and resistor power for LEDs in series. Select the next higher E12 standard resistor value.

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Calculation inputs

Change any value for an instant recalculation.

Calculation inputs are saved locally in your browser.

How is it calculated?

R = (supply voltage − LED count × forward voltage) / I, with I in amperes. We choose the next higher standard E12 resistance to keep the nominal current at or below target.

Resistor power: P = I² × R. Check power-source variation, component tolerances and thermal safety margins before building a circuit.

Frequently asked questions

Can I use one resistor value for every LED?

No. Forward voltage, current and circuit configuration matter.

Should multiple parallel LED branches share a resistor?

Normally each parallel LED branch should have its own current limiting arrangement.

Equipment related to this calculation

Practical, non-promotional buying considerations. Future partner recommendations will be clearly disclosed.

E12 / E24 resistors

Choose a standard resistor value and appropriate power rating for a low-voltage LED circuit.

Multimeter

Check voltages and resistance before wiring. This calculator is not for mains-voltage LED circuits.

Frequently asked questions

Why does an LED need a resistor?

A resistor limits current through the LED. Choose it based on supply voltage, LED forward drop and desired current.

Can I use this for mains-powered 120/230 V LEDs?

No. This calculator is for basic low-voltage circuits. Working directly with mains power is dangerous.