There are different materials or alloys out there which are used for heating coils, for vaping the most used are:

NiChrome, Kanthal D and Kanthal A. They all come in different thicknesses and each has a specific resistance per square millimeter per meter.

It can get confusing, because people who describe their coils use different material and measurements.

Basically, what we want to do is to transfer energy into the wire so that it heats up and vaporizes the liquid. More power roughly equals more vape. There is more to it, of course.

Power is expressed in Watts. Ohms law tells us that power in Watts equals the square of the voltage in Volts multiplied by the resistance in Ohms. To get more power you will need higher resistance or higher voltage.

Thinner wires have a higher resistance than thicker wires - you can think of them as you would think of water tubes. It is harder to force the same amount of water through a straw than through a fire hose.

The longer the heating wire is, the higher the resistance will be.

Here are some values for the different materials and sizes of wire:

Kanthal D 0.20mm -> 43.8 Ohms per Meter

Kanthal A1 0.20mm -> 45.3 Ohms per Meter

typical NiChrome 0.20mm -> 34.4Ohms per Meter

Kanthal D 0.16mm -> 66.9 Ohms per Meter

Kanthal A1 0.16mm -> 69.8 Ohms per Meter

typical NiChrome 0.16mm -> 50.0 Ohms per Meter

You see that the type and size of wire used is significant. You cant just take 2 centimeters of any wire and get the same result.

Some more trivia:

Thinner wire heats faster than thicker wire

Thinner wire gets hotter with the same power than thicker wire

The smallest coil I ever found working well was out of 0.08 mm Kanthal D, It was only one and a half turns around the wick. You don't need a really long coil

Europeans use Kanthal D while Americans use Kanthal A1 - no idea why