Led Resistor Calculator
Calculate the correct resistor value for your LED circuit. Input supply voltage, LED forward voltage, and LED current to get the resistor value, power dissipation, and nearest standard resistor value.
Published by:
isCalculator Editorial Team
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How to use this tool?
This calculator determines the correct resistor value for an LED circuit.
- Enter Source Voltage (V): The voltage of your power supply (e.g., 5V, 9V).
- Enter LED Forward Voltage (V): The LED's voltage drop (e.g., 2V for red, 3.3V for white).
- Enter LED Current (mA): The desired current in milliamps (e.g., 20mA).
- Click "Calculate".
Results:
- Resistor Value: The exact calculated resistance in ohms (Ω).
- Power Dissipation: The resistor's power rating needed (in watts).
- Nearest Standard Value: The closest standard resistor value you can buy.
- Formula Explanation: Shows the calculation steps.
Note: Forward voltage must be less than source voltage. All values must be positive.
Previous Results
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Frequently Asked Questions
It calculates the resistor value needed to limit current through an LED to prevent damage.
Enter the source voltage, LED forward voltage (typically 2V for red, 3V for blue/white), and desired current (usually 20mA). Click calculate.
Standard values are from the E12 series (e.g., 10, 12, 15, 18, 22, 27, 33, 39, 47, 56, 68, 82 ohms and multiples). The calculator picks the nearest.