LED Resistor Calculator
Series resistor value and power for any LED.
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Introduction
LED Resistor Calculator — Series resistor value and power for any LED. Enter Supply voltage (V), LED forward voltage (V), LED current (mA) to get an instant, accurate result.
Formula
Resistance = (supply voltage − LED forward voltage) / LED current. Power = (supply − forward voltage) × current.
Step-by-step
- Enter the Supply voltage (V).
- Enter the LED forward voltage (V).
- Enter the LED current (mA).
- Click Calculate to see your result instantly.
Real-world example
Example: With Supply voltage (V) = 9, LED forward voltage (V) = 2, LED current (mA) = 20, the LED Resistor Calculator gives Resistance Ohms: 350, Power Mw: 140.
Frequently Asked Questions
Where do I find my LED's forward voltage and current?
Check the LED's datasheet — common values are around 2V forward voltage and 20mA current for standard indicator LEDs.
What happens if the resistor value is too low?
Too little resistance lets excess current through, which can burn out the LED.
What inputs does the LED Resistor Calculator need?
You'll need to provide: Supply voltage (V), LED forward voltage (V), LED current (mA). All fields use sensible defaults, so you can see a working example immediately and then adjust the values to match your own numbers.
How accurate is the LED Resistor Calculator?
The LED Resistor Calculator applies the formula exactly as calculated — Resistance = (supply voltage − LED forward voltage) / LED current. Power = (supply − forward voltage) × current. — so results are precise for the inputs you provide. Accuracy depends on entering correct, realistic input values.
Is the LED Resistor Calculator free to use?
Yes, the LED Resistor Calculator is completely free, requires no signup, and runs instantly in your browser.
About the LED Resistor Calculator
The LED Resistor Calculator uses a real, verifiable formula — Resistance = (supply voltage − LED forward voltage) / LED current. Power = (supply − forward voltage) × current. — so results are accurate every time, not an approximation.