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Enter the data and press the button to do the calculation.
Online Calculator
LED resistor calculator
Enter the supply voltage, LED forward voltage, target current, and number of LEDs in series.
Ideal calculation. For a real circuit, choose a standard resistor value and a power rating with sufficient headroom.
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Frequently asked questions
What is the formula for an LED resistor?
R = (Vs - sum of Vf) / I.
What current should I enter?
The target current indicated for the LED or circuit, expressed in mA.
Is the calculated power the minimum rating I should buy?
It is the theoretical power dissipation. In practice, choose a resistor with a power rating that provides some headroom.
Can I connect multiple LEDs in series?
Yes, as long as the supply voltage exceeds the sum of their voltage drops.