LED Series Resistor Calculator
Find the series resistor and power dissipation for one or more LEDs from supply voltage, forward voltage, and current.
Series resistor (ideal)–
Nearest standard (≥, E12)–
Resistor power–
LED power–
Total power–
Sizing an LED resistor
R = (V_supply − n × V_f) / I
P_resistor = (V_supply − n × V_f) × I
An LED needs a series resistor to limit its current. The resistor drops the difference between the supply and the LED's forward voltage (multiplied by the number of LEDs in series), at the target current. Pick thenext standard value at or above the ideal resistance so you never exceed the rated current, and choose a resistor power rating comfortably above the calculated dissipation.
The supply must be higher than the total forward voltage (n × V_f); otherwise the LEDs can't light and no resistor value will work.