Find the Right Resistor for Any LED
A free browser-based LED resistor calculator that determines the correct current-limiting resistor for any LED circuit. Includes color presets with typical forward voltages, series and parallel array support, power dissipation warnings, and nearest E24 standard value matching.
Calculate current-limiting resistors for single LEDs and arrays instantly
Features
How to Calculate an LED Resistor
- Set supply voltage and LED specs. Enter the supply voltage (e.g. 5V, 12V) and select an LED color preset or enter custom Vf and If values.
- Choose configuration. Select single LED, series (LEDs in a chain), or parallel (LEDs side by side). Set the number of LEDs.
- Read the result. See the calculated resistance, nearest standard value, power dissipation, and any warnings about exceeding resistor ratings.
FAQ
How is the LED resistor calculated?
R = (Vs - Vf) / If. For series LEDs: R = (Vs - n×Vf) / If. The supply voltage minus the total LED voltage drop, divided by the desired current.
What are typical LED forward voltages?
Red: 1.8-2.2V, Orange: 2.0-2.2V, Yellow: 2.0-2.4V, Green: 2.0-3.5V, Blue: 3.0-3.5V, White: 3.0-3.5V, UV: 3.3-3.8V, IR: 1.2-1.5V.
What is the difference between series and parallel?
Series: LEDs share the same current, voltages add up. You need Vs > sum of all Vf. Parallel: each LED has its own resistor (or shared with same Vf), current multiplies.
Why does the resistor get hot?
The resistor converts excess voltage to heat. P = (Vs-Vf)×If. If power exceeds the resistor rating (typically ¼W for small resistors), it can overheat and fail.
Can I run LEDs without a resistor?
Only if the supply voltage exactly matches the LED forward voltage. In practice, this is risky — even small voltage variations can destroy the LED. Always use a resistor.
We can — and it's free! Just send us a quick message with your idea. If you'd like to discuss it in detail, leave your email and we'll get back to you. You can stay anonymous.
