Calculate the exact series resistor value and power rating for your LED circuit. Enter supply voltage, LED forward voltage, current, and LED count to get the resistor value, power dissipation, and nearest standard E12 resistor instantly.
Power: P = I_f² × R
E12 Standard Values: 1.0, 1.2, 1.5, 1.8, 2.2, 2.7, 3.3, 3.9, 4.7, 5.6, 6.8, 8.2 × 10n Ω
When connecting LEDs to a power source, a current-limiting resistor is essential to prevent the LED from burning out. This calculator helps you find the right resistor value and power rating for your LED circuit.
The calculator uses the formula R = (V_supply - N × V_f) ÷ I_f, where V_supply is your power supply voltage, V_f is the LED forward voltage (typically 1.8-3.3V depending on color), I_f is the desired current (typically 5-20mA), and N is the number of LEDs connected in series.
The calculator also recommends the nearest standard E12 resistor value and suggests a safe power rating (typically 2× the calculated power dissipation for reliability).
Forward voltage (Vf) is the minimum voltage required for an LED to conduct and emit light. Typical values: Red (1.8-2.2V), Green (2.0-2.4V), Blue/White (3.0-3.3V), Yellow (2.0-2.2V).
Standard LEDs typically operate at 10-20mA for full brightness. Higher currents increase brightness but reduce lifespan and generate more heat. Always check your LED datasheet for the maximum rating.
E12 is a standard resistor series with 12 values per decade (1.0, 1.2, 1.5, 1.8, 2.2, 2.7, 3.3, 3.9, 4.7, 5.6, 6.8, 8.2). These are commonly available and sufficient for most LED applications.
Yes, you can connect LEDs in series. The total voltage drop across all LEDs must be less than your supply voltage. The remaining voltage is dropped across the resistor.
Too low resistance → excessive current → LED burns out quickly. Too high resistance → insufficient current → LED is dim or does not light.