Use this calculator to easily find the optimal resistance value needed to limit the current flowing through an LED. Simply enter the system voltage and the LED’s recommended forward current (in milliamps, mA) and forward voltage drop as supplied by its datasheet. Then click the “Calculate” button and voila.

How does this calculator work? First, the total resistance required to limit the current in a wire to the LED’s recommended forward current is calculated using Ohm’s law assuming the wire is supplied with a voltage equal to the system voltage. Next, the resistance of the LED is calculated using its forward voltage drop and forward current values. Finally, the value of the current limiting resistor is calculated by subtracting the LED’s resistance from the total resistance needed to limit the LED’s current calculated above.