About the LED Resistor Calculator Online Free Tool

The LED Resistor Calculator Online Free Tool estimates the series resistor and resistor wattage for a single LED path from supply voltage, LED forward voltage, and target current.

How to Use the LED Resistor Calculator Online

1. Enter supply voltage and LED forward voltage.
2. Enter the target LED current in milliamps.
3. Run the calculator and choose a nearby standard resistor with suitable wattage.

Choosing Options Correctly

Use LED datasheet values and derate power for heat. For multiple LEDs in series, enter their total forward voltage. Constant-current drivers need a different design approach.

Common Use Cases

• Size an indicator LED resistor.
• Check resistor wattage for a prototype.
• Compare current targets for brightness and heat.

Quick FAQ

Why must supply voltage exceed forward voltage?
The resistor needs voltage headroom to set current. If supply voltage is too close to LED forward voltage, current becomes unstable.

Should I use the exact calculated resistor?
Usually choose the nearest standard value that gives a safe current, then check resistor wattage and LED brightness.

Can I use this for multiple LEDs?
Yes for simple series strings if you enter the total forward voltage. Parallel LED branches should usually have separate resistors.

What else affects LED current?
LED forward voltage changes with color, temperature, manufacturing tolerance, and current, so leave margin instead of designing at the absolute limit.