LED Series Resistor Calculator

Utilize this tool to determine the necessary resistance for driving one or more LEDs connected in series from a given voltage source while maintaining a specified current level.

Voltage of Power Source (V):

Forward Voltage of LED (V):

Forward Current of LED (mA):

LED Forward Voltage Ranges

LED Color	Forward Voltage (Vf) Range	Typical Forward Current (mA)
Red	1.8V - 2.2V	20 - 30 mA
Orange	1.8V - 2.2V	20 - 30 mA
Yellow	2.0V - 2.4V	20 - 30 mA
Green	2.0V - 3.0V	20 - 30 mA
Blue	2.7V - 3.5V	20 - 30 mA
White	3.0V - 3.6V	20 - 30 mA

LED Series Resistor Calculation

The formula to calculate the value of the series resistor in an LED circuit is based on Ohm's Law, which states:

V = I * R

Where:

V is the voltage drop across the resistor (in volts),
I is the current flowing through the circuit (in amperes), and
R is the resistance of the resistor (in ohms).

In an LED circuit, the voltage drop across the resistor (V_R) can be calculated by subtracting the forward voltage of the LED (V_f) from the supply voltage (V_s). So, the formula becomes:

V_R = V_s - V_f

Then, using Ohm's Law, you can calculate the resistance (R) of the resistor required to limit the current (I) flowing through the circuit to the desired value. Rearranging the formula gives:

R = V_R / I

Where I is the desired current in the circuit (usually specified in milliamperes, mA).

So, to summarize:

Calculate the voltage drop across the resistor (V_R) by subtracting the forward voltage of the LED (V_f) from the supply voltage (V_s).
Use Ohm's Law to calculate the resistance (R) of the resistor required to limit the current (I) flowing through the circuit to the desired value.