LED Resistor Calculator
Calculate the resistance and power rating required for your LED circuit.
Required Resistance:
Power Dissipation:
Recommended Resistor Wattage:
How to Use the LED Resistor Calculator
Light Emitting Diodes (LEDs) are current-dependent devices. If you connect an LED directly to a power source like a battery or power supply without a resistor, the LED will draw too much current and burn out almost instantly. This calculator helps you determine the specific resistor value needed to limit the current to a safe level.
The LED Resistor Formula
The calculation is based on Ohm's Law (V = I × R). To find the resistance (R), we use the following formula:
R = (Vs – Vf) / I
- Vs: Source Voltage (The voltage of your power supply).
- Vf: Forward Voltage (The voltage drop across the LED).
- I: Forward Current (The desired current in Amperes, usually 0.02A for standard LEDs).
Common LED Forward Voltage Reference
| LED Color | Typical Forward Voltage (V) | Typical Current (mA) |
|---|---|---|
| Red | 1.8V – 2.2V | 20mA |
| Yellow / Orange | 2.0V – 2.2V | 20mA |
| Green | 2.1V – 3.4V | 20mA |
| Blue / White | 3.0V – 3.6V | 20mA |
Example Calculation
Suppose you have a 9V battery and you want to light up a Red LED (Forward Voltage of 2.0V) at a current of 20mA (0.02 Amps).
Calculation: (9V – 2.0V) / 0.02A = 7V / 0.02A = 350 Ohms.
The power dissipation would be 7V × 0.02A = 0.14 Watts, meaning a standard 1/4 watt (0.25W) resistor would work perfectly.