About LED Series Resistor Calculator
Calculate the required current-limiting resistor value and wattage rating for LEDs.. Designed for accurate, instantaneous calculations with zero wait time.
Formula
Resistor R = (Source Voltage - LED Voltage) / LED Current
Example Calculation
Connecting a 2.0V red LED to a 9V battery at 20 mA requires a 350 Ω resistor (0.14 W).
How to Use
- Enter your values into the form fields above.
- The calculation updates immediately in real time.
- Inspect the main summary and secondary breakdowns below.