Current doesn't equal what I expected
Now I have a 6 volt battery, 220 Ohms resistor, and a LED. Now I can calculate the current. So I divided the total volt (6v) with the total resistance (220 Ohms). But this gave me 6v / 220 Ohms = 27mA. 27mA does not equal 18mA, which the LED needs to work.


Your math is wrong. Mainly, the resistance of the led is negligible, so it can be ignored, but the voltage drop can not.







simulate this circuit &ndash; Schematic created using CircuitLab

The voltage across the resistor is what sets the current, not the total voltage.
This can be tested with a multimeter.