LED Resistor Calculator
Find the current-limiting resistor value needed for an LED circuit.
Resistor value
150 Ω
Nearest E12 standard value: 150 Ω
Resistor power dissipation: 0.06 W
Suggested resistor wattage: 0.125W
Usage examples
Wiring an LED to a microcontroller like Arduino
Instantly find the current-limiting resistor needed to connect a single LED to a 5V or 3.3V board.
Wiring several LEDs in series
Calculate the resistor needed to safely drive multiple LEDs in series from a given supply, such as a battery.
Checking a resistor's heat margin
See the calculated resistor's power dissipation so you can pick a wattage rating that won't overheat.
Frequently asked questions
Is what I enter sent to a server?
No. All calculations happen entirely in your browser and are never sent to a server.
What exactly is an LED's forward voltage (Vf)?
It varies a bit by LED color, manufacturer, and chip. The color presets here are typical datasheet values; check your specific LED's datasheet if you need precision.
What if there's no resistor exactly matching the calculated value?
The nearest standard E12 resistor value is shown alongside the exact calculation. Picking a slightly higher resistance protects the LED (at the cost of being a bit dimmer).
Can I wire LEDs in parallel instead?
This calculator assumes a series connection. If wiring LEDs in parallel, it's safer to give each LED its own resistor, since individual LED variation can cause current to split unevenly across a shared one.