LED Resistor Calculator
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.
How to use LED Resistor Calculator
- Enter your supply or battery voltage in volts.
- Enter the LED forward voltage and the target forward current, usually 20 mA for a standard LED.
- Read the exact resistor value, the nearest E12 size and the minimum power rating.
- Pick a real resistor at or above the suggested wattage.
Frequently asked questions
What formula does this LED resistor calculator use?
It applies Ohm's law to the voltage across the resistor, so R equals the supply voltage minus the LED forward voltage, divided by the LED current in amps.
Why does it show a nearest E12 resistor value?
Real resistors only come in standard series such as E12, so the tool rounds your exact ohms up to the closest common size that keeps LED current at or below your target.
How is the resistor power rating worked out?
It multiplies the voltage dropped across the resistor by the current through it, giving the watts the resistor must dissipate so you can pick a part rated safely above that.
What is LED Resistor Calculator?
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.
Is LED Resistor Calculator free to use?
Yes. LED Resistor Calculator is completely free, with no sign-up and no usage limits.
Does LED Resistor Calculator work in a web browser?
Yes. LED Resistor Calculator runs in any modern web browser. There is nothing to download or install.
Is my data private with LED Resistor Calculator?
Yes. LED Resistor Calculator runs entirely on your device in your browser, so nothing you enter is uploaded to a server.
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