LED Resistor Calculator

Picking the current-limiting resistor for an LED, or a series string of them, off a fixed supply is simple in principle and easy to get wrong in practice once forward voltage and target brightness current are factored in. This calculator sizes the series resistor for one or more LEDs in series, so status and indicator LEDs land at the right brightness without over-driving them.

LED Series Resistor

Current-limiting resistor for one or more LEDs in series off a fixed supply

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Supply voltage

LED forward voltage

At your target current — check the datasheetLEDs in series

Target current

Series resistor (exact)

150 Ω

Nearest E24 value

150 Ω

Actual current at nearest value

20.0 mA

Resistor power dissipation

60.0 mW

Total LED forward voltage

2.00 V

For RGB or multi-color LEDs, each color typically has a different Vf and needs its own resistor even when driven from the same supply and switched together.