Led Resistor Calculator
Calculate the correct current-limiting resistor for an LED from supply voltage, forward voltage and desired current. Standard E12 values included in output.
Last updated: May 2026
Enter valid source, LED voltage and current
Typical single LED current is 5 mA to 20 mA.
Why this calculator is useful
Use this page when you want a safe resistor value for a basic LED circuit rather than guessing and risking too much current. The point is not to replace proper design review. The point is to catch obvious mismatches quickly and keep small electronics tasks moving. That is especially helpful in hobby work, repair work and prototype setups where you want a fast answer without opening a full simulator.
A calculator like this earns its place because it reduces the chance of a simple arithmetic mistake creating a bigger bench problem later. Calculate first, then measure on the real circuit.
Typical use cases
- indicator LEDs, breadboard tests and simple hobby wiring
- Reading and sanity-checking datasheet examples
- Confirming values before soldering or ordering parts
The final circuit still depends on tolerances, load conditions and the actual parts in front of you, but a quick page like this gives you a reliable starting point.
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Frequently Asked Questions
How do I choose the right LED resistor value?
The resistor controls current through the LED using Ohm's Law: R = (Supply Voltage - LED Forward Voltage) / LED Current. Too small a resistor delivers too much current and kills the LED instantly. Too large a resistor dims the LED or prevents it from lighting. This calculator finds the safe middle ground for reliable indicator lights and hobby circuits.
What happens if the resistor is too small or too large?
Too small (underestimated): LED draws excessive current (e.g., 100 mA instead of 20 mA), overheats, and fails in seconds—often permanently. Too large: LED draws minimal current and either doesn't light or glows very dimly. A typical indicator LED needs 5–20 mA to be visible; hobby LEDs work well at 10–15 mA.
Does LED forward voltage differ by color?
Yes. Red LEDs drop ~2.0V, yellow/amber ~2.1V, green ~2.2V, blue/white ~3.0–3.5V. Using the wrong forward voltage creates the wrong resistor value. A blue LED on 5V needs a much smaller resistor than a red LED on the same supply because the voltage drop available for the resistor is different (1.5V remaining vs 3V remaining).
Does the calculator work for different power supplies?
Yes. 5V, 12V, 24V, even wall power circuits—the math is the same. But verify your supply voltage first. A mistake here propagates into the resistor value. Also consider supply ripple and tolerance: a "5V" supply might be 4.75–5.25V, affecting the actual resistor value slightly.
Should I use the exact calculated resistor value?
No. Use the nearest standard resistor value (E12 or E24 series). A calculation giving 470Ω is perfect; a calculation giving 463Ω rounds up to 470Ω (closer is safer because it slightly reduces current). Always round up (smaller resistor) rather than down when the exact value isn't available—overshooting the current slightly is safer than undershooting.