Enter the supply voltage, forward voltage drop, and forward current into the calculator to determine the resistance of the current limiting resistor.

Current Limiter Resistor Formula

The following formula is used to calculate the value of a current limiting resistor.

R = (V - Vf) / If

Variables:

  • R is the resistance of the current limiting resistor (Ohms) V is the supply voltage (Volts) Vf is the forward voltage drop across the LED (Volts) If is the forward current through the LED (Amperes)

To calculate the resistance of the current limiting resistor, subtract the forward voltage drop across the LED from the supply voltage. Then divide the result by the forward current through the LED.

What is a Current Limiter Resistor?

A Current Limiter Resistor is a component used in electrical circuits to control or limit the amount of current flowing through the circuit. It works by providing a specific amount of resistance, which in turn reduces the current to a safe level. This is crucial in preventing damage to sensitive components within the circuit that may not be able to handle high levels of current. The value of the resistor is chosen based on the desired current limit and the voltage across it.

How to Calculate Current Limiter Resistor?

The following steps outline how to calculate the resistance of a current limiting resistor using the formula: R = (V – Vf) / If.


  1. First, determine the supply voltage (V) in volts.
  2. Next, determine the forward voltage drop across the LED (Vf) in volts.
  3. Next, determine the forward current through the LED (If) in amperes.
  4. Next, substitute the values of V, Vf, and If into the formula: R = (V – Vf) / If.
  5. Finally, calculate the resistance (R) of the current limiting resistor.
  6. After calculating the result, check your answer with the calculator above.

Example Problem:

Use the following variables as an example problem to test your knowledge:

Supply voltage (V) = 12 volts

Forward voltage drop across the LED (Vf) = 2 volts

Forward current through the LED (If) = 0.02 amperes