Online LED resistance calculator using Ohm's Law
Online electrical calculator to measure the resistance of a LED resistor circuit using the Ohm's Law.
The formula to calculate the resistance is:
The following circuit explains the formula.
Where power supply voltage (Vs) is the voltage of the power supply, e.g. a 9 volt battery, LED voltage drop (Vf) is the forward voltage drop across the LED, and LED current (I) is the desired current of the LED. The above formula requires the current in amperes, although this value is usually given by the manufacturer in milliamperes, such as 20 mA.