LED Resistor Calculator
Series resistor value for an LED.
V
V
mA
How it works
R = (supply voltage − total LED forward voltage) ÷ LED current. Power in the resistor = I² × R. Pick the next higher standard resistor value and a wattage rating at least twice the calculated power. A dash means the supply is too low for that many LEDs. Example: with the default values, resistor value comes to 500 Ω.
FAQ
Is this calculator free?
Yes. No signup is needed and nothing you enter is stored.
Is the result exact?
Results are rounded for display. For financial, medical, or legal decisions, confirm with a professional.
Do my numbers leave my device?
No. The calculation runs in your browser.