Every LED needs a series resistor to limit its current, otherwise it draws too much and burns out. This calculator works out the correct resistor from three numbers: your supply voltage, the LED forward voltage from its datasheet, and the target forward current. It uses the standard formula R equals the supply voltage minus the forward voltage, all divided by the current in amps. It then rounds up to the nearest common E12 resistor value so you can grab one from your parts drawer, and it tells you the power the resistor will dissipate so you can pick a part with a safe wattage rating. Typical indicator LEDs want around ten to twenty milliamps at a forward voltage near two volts for red or three volts for blue and white. Enter your values and read the answer instantly in your browser.
Every LED needs a series resistor to limit its current, otherwise it draws too much and burns out. This calculator works out the correct resistor from three numbers: your supply voltage, the LED forward voltage from its datasheet, and the target forward current.
Yes. LED Resistor Calculator is completely free, with no sign-up and no usage limits.
Yes. LED Resistor Calculator runs in any modern web browser. There is nothing to download or install.
Yes. LED Resistor Calculator runs entirely on your device in your browser, so nothing you enter is uploaded to a server.