Size a Current-Limiting Resistor for an LED
Work out the resistor value an LED needs from supply voltage and current.
💡 Ohm's law: V = I × R. Power adds P = V × I. Knowing any two lets you derive the rest — handy for sizing resistors, checking LED current, or working out heat dissipation.
LEDs tips
Resistor value R = (supply V − LED forward V) ÷ LED current. Enter the voltage drop and target current to get R.
A typical LED wants ~20mA (0.02A). With a 5V supply and a 2V LED, that needs ~150Ω.
Check the power too — the calculator shows watts so you can pick a resistor that won't overheat.
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