Compute Proper Resistor for LEDs Remember, this is not the best way to power an LED because the resistor eats current.  It is useful for testing LEDs and making sure you don't burn them out in the process. Source Voltage = LED Forward Voltage Drop = LED Forward Current in Milliamps = Needed Resistance in Ohms = Using Closest Standard 5% Resistor Closest Standard 5% Resistor = Closest Standard 5% Resistor Wattage = Actual Current = Actual Power Dissipated By LED = Actual Power Dissipated By Resistor =