LED Resistor Calculator

The LED Resistor Calculator is a handy tool designed to simplify the process of determining the appropriate resistor value for driving LEDs. By inputting the power supply voltage, LED forward voltage, and desired forward current, this calculator quickly calculates the resistor value needed to ensure safe and optimal LED operation.

LED Resistor Calculator

LED Resistor Calculator Tool

Voltage Drop and Recommended Resistor Size for Various Color LEDs

LED ColorForward Voltage (Vf)Recommended Resistor Size (Ohms) for 20mA Forward Current
Red1.8 – 2.2(Supply Voltage – Vf) / 0.02
Green2.8 – 3.5(Supply Voltage – Vf) / 0.02
Blue3.0 – 3.7(Supply Voltage – Vf) / 0.02
Yellow1.8 – 2.2(Supply Voltage – Vf) / 0.02
White3.0 – 3.7(Supply Voltage – Vf) / 0.02

How to Calculate the Size of Resistor to Use with an LED

Calculating the size of the resistor to use with an LED involves considering the LED’s forward voltage (Vf) and the desired forward current (If). Here’s the general formula to calculate the resistor value:

Resistor Value (R) = (Power Supply Voltage (V) – LED Forward Voltage (Vf)) / Forward Current (If)

To calculate the resistor value, follow these steps:

  1. Determine the Power Supply Voltage (V): This is the voltage that will be provided to the LED circuit. It can be the voltage of a battery or the output voltage of a power supply.
  2. Identify the LED Forward Voltage (Vf): Each LED has a specific forward voltage, which is the voltage required for it to function properly. You can usually find this information in the LED’s datasheet or product specifications.
  3. Decide on the Desired Forward Current (If): The forward current determines the brightness and efficiency of the LED. You can choose a suitable forward current based on your requirements or the LED’s specifications.
  4. Calculate the Resistor Value (R): Plug the values into the formula mentioned earlier to calculate the resistor value. The result will be in ohms.
  5. Select the Standard Resistor Value: After calculating the resistor value, you need to choose a standard resistor value that is closest to the calculated value. Common resistor values include E6, E12, or E24 series.
  6. Verify Power Rating: Ensure that the selected resistor has an appropriate power rating to handle the power dissipation. You can calculate the power (P) using the formula: P = I^2 * R, where I is the forward current and R is the resistor value. Select a resistor with a power rating higher than the calculated power to prevent overheating.

Keep in mind that the calculated resistor value is an approximation, and you should choose the nearest standard resistor value available in the market.