LED Resistor Calculator
Calculate the correct resistor value for an LED circuit.
Enter source voltage, LED forward voltage, and desired current.
Required Resistor
LED Resistor Formula (from Ohm’s Law):
R = (V_source - V_led) / I_led
Where:
- R = resistance needed (ohms)
- V_source = supply voltage (V)
- V_led = LED forward voltage (V)
- I_led = desired LED current (A)
Typical LED forward voltages:
- Red: 1.8–2.2V
- Orange/Yellow: 2.0–2.2V
- Green: 2.0–3.5V
- Blue/White: 3.0–3.6V
- Infrared: 1.2–1.6V
Typical LED current: 20 mA (0.020A) for standard LEDs, 350 mA for high-power LEDs.
Power dissipated by resistor:
P = (V_source - V_led) × I_led
Always choose a resistor with a power rating above the calculated dissipation.