Resistor Calculator

Combine resistors in series and parallel, and find the series resistor for an LED.

Read the full Resistor Calculator guide →

Resistor 1(Ω)Resistor 2(Ω)Supply voltage (for LED)(V)LED forward voltage(V)LED current(mA)

How the Resistor Calculator works

Series resistances add; parallel resistances add as reciprocals. For LEDs, the series resistor sets the current — skip it and the LED dies in milliseconds.