How this calculator works
Enter the values for first value, second value and review the units before calculating.
Formula / method
R = (Vs − Vf) ÷ I
Worked example
A 9 V supply, 2 V LED and 20 mA target require 350 Ω ideally.
Assumptions and limitations
Current is converted from milliamps to amps and the LED is used in a simple series circuit.
Choose a standard resistor with adequate power rating and verify actual LED behavior.