LED Resistor Calculator
Calculate the correct resistor for your LED circuit with an interactive SVG circuit diagram. Select from 8 LED types and 5 voltage presets, configure series or parallel connections, and get the nearest E24 standard value with power dissipation warnings β free, no sign-up required.
Source Voltage
LED Type
LED Configuration
Circuit Diagram
Result
What is an LED Resistor Calculator?
An LED resistor calculator determines the correct resistor value needed to safely limit current through an LED. Without the proper resistor, an LED will draw too much current and burn out. This tool calculates the ideal resistance using Ohm's Law: R = (Vsource - Vf) / If.
How to Calculate LED Resistor Values
- Select your power source voltage (3.3V, 5V, 9V, 12V, or custom)
- Choose your LED type or enter custom forward voltage and current values
- Set the number of LEDs and connection type (series or parallel)
- View the calculated resistance and nearest standard E24 value
- Check the power dissipation and recommended resistor wattage
Frequently Asked Questions
Why do LEDs need a resistor?
LEDs are current-driven devices with very low internal resistance. Without a current-limiting resistor, the LED will draw excessive current, overheat, and burn out almost instantly.
Should I connect LEDs in series or parallel?
Series connection uses one resistor for all LEDs but requires higher voltage. Parallel connection uses one resistor per LED branch but works with lower voltages. Series is more efficient; parallel provides uniform brightness.
What happens if I use the wrong resistor value?
A resistor that is too small allows too much current, shortening LED life or burning it out. A resistor that is too large limits current too much, making the LED dim or not light up at all.
Can I power LEDs directly from Arduino GPIO pins?
Yes, but with limitations. Arduino GPIO pins can source about 20mA at 5V, which is enough for one standard LED with a resistor. For multiple LEDs or high-power LEDs, use a transistor or MOSFET.