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
Try the related tool and calculate your own values instantly.
Open LED Resistor Calculator