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Size a Current-Limiting Resistor for an LED

Work out the resistor value an LED needs from supply voltage and current.

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Enter any two values and the other two are solved automatically

πŸ’‘ Ohm's law: V = I Γ— R. Power adds P = V Γ— I. Knowing any two lets you derive the rest β€” handy for sizing resistors, checking LED current, or working out heat dissipation.

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Resistor value R = (supply V βˆ’ LED forward V) Γ· LED current. Enter the voltage drop and target current to get R.

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A typical LED wants ~20mA (0.02A). With a 5V supply and a 2V LED, that needs ~150Ξ©.

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Check the power too β€” the calculator shows watts so you can pick a resistor that won't overheat.

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