LED Resistor Calculator
Calculate the resistor needed for a single LED.
Formula
R = (Vs − Vf) / I.
How to Choose an LED Resistor
A series resistor limits current through an LED by dropping the voltage difference between the supply and the LED forward voltage.
Example Calculation
With a 5 V supply, a 2 V LED and a target current of 15 mA, R = (5 − 2) / 0.015 = 200 Ω.
Factors and Interpretation
LED forward voltage varies by color, current and temperature. Choose a nearby standard resistor value, often rounding upward to reduce current, and verify the resistor power rating.
Frequently Asked Questions
Why is current entered in mA?
LED currents are commonly specified in milliamps; the calculator converts mA to amps internally.
Can I use one resistor for multiple parallel LEDs?
Separate resistors are generally preferred because LED current may not divide evenly.
What if supply voltage is lower than LED forward voltage?
The simple resistor method will not provide the intended operating current.
Related Tools
Formula and Practical Limits
A series LED resistor is commonly estimated from supply voltage minus LED forward voltage, divided by desired current. Forward voltage varies with LED type, temperature and current, so practical designs should allow margin and respect component ratings.