Why LEDs need resistors
An LED is a current-driven component. Without current limiting, the LED may draw too much current and fail.
Formula
The common formula is R = (Vsupply - Vf) / I.
Example
For a 5 V supply, a 2 V red LED and 20 mA current, the resistor is (5 - 2) / 0.02 = 150 Ω.
Power rating
The resistor also dissipates power. In the example, P = I² × R = 0.06 W.
Practical design notes
For high-power LEDs, use a constant-current LED driver instead.
Use the calculator
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Open LED Resistor CalculatorFrequently asked questions
What is covered in How to Calculate an LED Resistor?
This guide explains the concept, formula, practical examples and design notes for electronics engineering work.
Can I use this guide for production hardware?
Use it for learning and early estimates. Production hardware should always be verified with datasheets, simulations and real measurements.
Is there a related calculator?
Yes. EngiCalc guides link to relevant calculators so you can test values directly in the browser.
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