💡 LED Resistor Calculator
Calculate resistor needed for LED circuits
How LED Resistor Calculation Works
Formula
R = (Vs - Vf) / I
- 1Enter the supply voltage (Vs), LED forward voltage (Vf), and desired current (I).
- 2The voltage across the resistor is Vs - Vf.
- 3Resistance = voltage drop / current (Ohm's Law).
- 4The calculator finds the nearest standard E24 resistor value.
- 5Actual current and power dissipation are calculated with the standard value.
About LED Resistor Calculator
Calculate the correct resistor value for an LED circuit. Enter supply voltage, LED forward voltage, and desired current. Shows nearest standard resistor value.
Frequently Asked Questions
What forward voltage does my LED have?
Common values: Red LEDs ~1.8-2.2V, Yellow/Green ~2.0-2.4V, Blue/White ~3.0-3.6V. Check the datasheet for exact values. Using the wrong value can burn out the LED.
What current should I use for an LED?
Standard LEDs typically run at 20mA. High-brightness LEDs may use 30-50mA. Always check the datasheet for the maximum current rating and stay below it.
What wattage resistor do I need?
Calculate power: P = (Vs - Vf) × I. For a 5V supply, 2V LED, and 20mA: P = 3V × 0.02A = 0.06W. A 1/8W (0.125W) resistor works, but 1/4W gives safety margin.