Probably a total noob question but here goes..
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Explain it to the Dumb Noob: Ohm's Law Calculations
- As simple as it is to use, some people have a tough time grasping the concept. Warning: Includes graphic photos of mod explosions.
- My attempt at explaining Ohm's Law in simple layman terms and how it relates to vaping.
Better to ask questions and you are doing a fantastic job of getting the education that so many need. Kudos to you!! 
It all pays off in two months time I'm making my own juice wrapping fused clapton coils blowing huge clouds O's and jellyfish. Just scratching the surface but all the research and questions followed with basic safety ohms law and half a brain I have been having the time of my life!Better to ask questions and you are doing a fantastic job of getting the education that so many need. Kudos to you!!
!I don't have a lot to add to what the others have said, but maybe I can put a different spin on it.
Keep in mind everything I am saying relates to kanthal, I have no experience with other metal types.
Like the others said, the higher the gauge number, the thinner the wire. The thinner the wire the more resistance it has. This means for a thinner wire it will take less wraps at a given coil diameter to reach a specific resistance. Thinner wire also heats up faster (less ramp up time). Thicker, or what is often called "heavier" wire will require more wraps at a given diameter to reach a specific resistance. Thicker wire also has a slower ramp up time, but it sort of depends on how thick, how low the resistance is and how many amps you are throwing at it.
What does this mean to the average vaper? It boils down to surface area and build deck size. And not just surface area of the wire, but more importantly the surface area in regards to how much of the wick it covers. In most cases the more surface area of the wick you heat up, the better the flavor could be. And sometimes this can be limited by the build deck. On a dripper you might have a lot of area to utilize letting you use a longer coil. In an RTA your space might be much more limited or you run the risk of shorting the coil out on the side of the chimney.
So for a given coil length and inner diameter the resistance you want to vape at will determine the size of wire you use. Let me give a few examples.
I normally vape at around 1.5 ohms and use 28 gauge kanthal. My normal coil is about 10-12 wraps around a 2mm shaft which gives me a 4mm long coil. This is a micro coil mind you, so no spacing between coils.
Now lets say I want to use a larger diameter wire for whatever reason. Maybe it is all I could find, maybe I heard it has more surface area and will have better taste (my opinion on that later).
If I want to stay at my 1.5 ohm resistance 26 gauge wire would be 17 wraps with a 7.5mm long coil
24 gauge wire would be 26 wraps at 14mm long.
As you can see, each time we go down 2 wire sizes the numbers double. And according to the calculator I used the amount of power needed for the coil increases as well, even though we are using the same resistance. Which makes sense because we are using longer lengths of wire that have less resistance, so they are harder to heat up. However the main concern is the two longer coils won't fit on the build deck of my tank. The 26 gauge might, and probably wouldn't be an issue in most RDA's. However the 24 gauge isn't going to fit in anything. You could go to a larger diameter coil ( the bit you use to wrap the coil around), that would shorten the length, but some tanks have issues with that too. I could most likely use a 3mm bit to wrap my coil and the 26 gauge would work, but still not the 24 gauge wire.
And if my goal was to have more surface area, I could just as easily use a spaced coil with the 28 gauge wire. There is no need to use a larger wire that takes longer to heat up.
Now lets say we wanted to go a different direction. Maybe I don't want to vape at 1.5 ohms anymore and I want to try something lower. Maybe I want a hotter vape and want to try something less than 1 ohm. Lets make it simple and say .5 ohms.
At .5 ohms 28 gauge wire is going to give me a coil with 3 wraps at a 1mm length. Take my word for it, DON'T try that. After 5 years of experimenting I can tell you what will happen. You are going to get really hot, really fast and burn your juice and probably burn your wick in half if you are using cotton. It is also not going to taste very good.
26 gauge wire will be 5 wraps with a 2mm long coil, better, but still not great. You could use a spaced coil and it would probably work pretty well.
24 gauge wire would be 8 wraps at 4.4mm, this would be better in my opinion. Give the coils a little spacing and it would probably be close to perfect.
So now you are going to either have to use larger wire, or try some kind of twisting, braiding or or other fancy coil build. If all you have is 28 gauge wire (like me) the easiest thing to do is just twist up two or three pieces in a drill and presto you have lower gauge wire. Or you could just buy a larger gauge wire to start with.
The lower you go in resistance, the larger the wire you are going to need. This why a lot of the really low ohm builds you see use some sort of fancy coil with multiple wires wrapped together in some fashion. It gives you lower resistance wire, and increases the surface area of the wire.
Ok, remember I said I had an opinion on wire surface area. I have played with it, and TO ME it doesn't seem to make a difference. I have tried some of the fancy coil builds and I didn't notice any difference in flavor at all. All I noticed was they were a pain to make (except twisting, that is pretty easy) and took a lot longer to heat up.
For me the length of the coil made a bigger difference than the actual surface area of the wire. Now if you are trying to make a .2 ohm coil, then ya I see a point to it. But for .5 to 1 ohm it just seems like more work than what its worth to me. If you want to do it, go for it, they do look pretty. Another way to lower your resistance is use a dual coil build if your build deck supports it. Again, personally I don't care for them. Tried it, didn't see a big difference other than using more wire and using up more juice.
Another good example of wire diameter choice is using temp control. I just started playing with it and didn't know much about it. I knew I couldn't use kanthal though. So I got some 28 gauge ni 200 wire. Come to find out your target resistance for a nickel temp control build is around .14 ohms. I discovered that to do that I need 12 wraps or more to get it, and they suggest spaced coils. That is a VERY hard build to get in any of my current tanks. I am either going to have to get a lower gauge wire so I have less wraps or try a different material. I am thinking stainless might be the way to go.
I don't know if any of that helps you any, but there it is anyway.
Keep in mind everything I am saying relates to kanthal, I have no experience with other metal types.
Like the others said, the higher the gauge number, the thinner the wire. The thinner the wire the more resistance it has. This means for a thinner wire it will take less wraps at a given coil diameter to reach a specific resistance. Thinner wire also heats up faster (less ramp up time). Thicker, or what is often called "heavier" wire will require more wraps at a given diameter to reach a specific resistance. Thicker wire also has a slower ramp up time, but it sort of depends on how thick, how low the resistance is and how many amps you are throwing at it.
What does this mean to the average vaper? It boils down to surface area and build deck size. And not just surface area of the wire, but more importantly the surface area in regards to how much of the wick it covers. In most cases the more surface area of the wick you heat up, the better the flavor could be. And sometimes this can be limited by the build deck. On a dripper you might have a lot of area to utilize letting you use a longer coil. In an RTA your space might be much more limited or you run the risk of shorting the coil out on the side of the chimney.
So for a given coil length and inner diameter the resistance you want to vape at will determine the size of wire you use. Let me give a few examples.
I normally vape at around 1.5 ohms and use 28 gauge kanthal. My normal coil is about 10-12 wraps around a 2mm shaft which gives me a 4mm long coil. This is a micro coil mind you, so no spacing between coils.
Now lets say I want to use a larger diameter wire for whatever reason. Maybe it is all I could find, maybe I heard it has more surface area and will have better taste (my opinion on that later).
If I want to stay at my 1.5 ohm resistance 26 gauge wire would be 17 wraps with a 7.5mm long coil
24 gauge wire would be 26 wraps at 14mm long.
As you can see, each time we go down 2 wire sizes the numbers double. And according to the calculator I used the amount of power needed for the coil increases as well, even though we are using the same resistance. Which makes sense because we are using longer lengths of wire that have less resistance, so they are harder to heat up. However the main concern is the two longer coils won't fit on the build deck of my tank. The 26 gauge might, and probably wouldn't be an issue in most RDA's. However the 24 gauge isn't going to fit in anything. You could go to a larger diameter coil ( the bit you use to wrap the coil around), that would shorten the length, but some tanks have issues with that too. I could most likely use a 3mm bit to wrap my coil and the 26 gauge would work, but still not the 24 gauge wire.
And if my goal was to have more surface area, I could just as easily use a spaced coil with the 28 gauge wire. There is no need to use a larger wire that takes longer to heat up.
Now lets say we wanted to go a different direction. Maybe I don't want to vape at 1.5 ohms anymore and I want to try something lower. Maybe I want a hotter vape and want to try something less than 1 ohm. Lets make it simple and say .5 ohms.
At .5 ohms 28 gauge wire is going to give me a coil with 3 wraps at a 1mm length. Take my word for it, DON'T try that. After 5 years of experimenting I can tell you what will happen. You are going to get really hot, really fast and burn your juice and probably burn your wick in half if you are using cotton. It is also not going to taste very good.
26 gauge wire will be 5 wraps with a 2mm long coil, better, but still not great. You could use a spaced coil and it would probably work pretty well.
24 gauge wire would be 8 wraps at 4.4mm, this would be better in my opinion. Give the coils a little spacing and it would probably be close to perfect.
So now you are going to either have to use larger wire, or try some kind of twisting, braiding or or other fancy coil build. If all you have is 28 gauge wire (like me) the easiest thing to do is just twist up two or three pieces in a drill and presto you have lower gauge wire. Or you could just buy a larger gauge wire to start with.
The lower you go in resistance, the larger the wire you are going to need. This why a lot of the really low ohm builds you see use some sort of fancy coil with multiple wires wrapped together in some fashion. It gives you lower resistance wire, and increases the surface area of the wire.
Ok, remember I said I had an opinion on wire surface area. I have played with it, and TO ME it doesn't seem to make a difference. I have tried some of the fancy coil builds and I didn't notice any difference in flavor at all. All I noticed was they were a pain to make (except twisting, that is pretty easy) and took a lot longer to heat up.
For me the length of the coil made a bigger difference than the actual surface area of the wire. Now if you are trying to make a .2 ohm coil, then ya I see a point to it. But for .5 to 1 ohm it just seems like more work than what its worth to me. If you want to do it, go for it, they do look pretty. Another way to lower your resistance is use a dual coil build if your build deck supports it. Again, personally I don't care for them. Tried it, didn't see a big difference other than using more wire and using up more juice.
Another good example of wire diameter choice is using temp control. I just started playing with it and didn't know much about it. I knew I couldn't use kanthal though. So I got some 28 gauge ni 200 wire. Come to find out your target resistance for a nickel temp control build is around .14 ohms. I discovered that to do that I need 12 wraps or more to get it, and they suggest spaced coils. That is a VERY hard build to get in any of my current tanks. I am either going to have to get a lower gauge wire so I have less wraps or try a different material. I am thinking stainless might be the way to go.
I don't know if any of that helps you any, but there it is anyway.
There is a wealth of knowledge in the Steam Engine blog and video
Steam Engine | free vaping calculators
Steam Engine | free vaping calculators
Most everything has been covered so I won't rehash it, but I do want to add a couple of things.
First the easiest way think about resistance vs size is to think of water hoses. Would a small garden hose be more or less resistant to water flowing through it than say a large fire hose? It is the same concept, the larger hose, the less resistance. The one caveat with wire is when changing wire types. The same size Kanthal is going to be more resistance than say the same size stainless steel wire.
As far as deciding what gauge to use, first decide on what you want your inside diameter of the coil to be, then use a vaping calculator to determine what wire type and gauge you should use to get 7 wraps at your desired resistance. I am not sure why but 7 wraps seems to be the optimum number of wraps (at least to me). Although if building on smaller decks you may not be able to get 7 wraps, so then calculate to get as close as you can to 7. I never go lower than 5 or more than 8 though.
First the easiest way think about resistance vs size is to think of water hoses. Would a small garden hose be more or less resistant to water flowing through it than say a large fire hose? It is the same concept, the larger hose, the less resistance. The one caveat with wire is when changing wire types. The same size Kanthal is going to be more resistance than say the same size stainless steel wire.
As far as deciding what gauge to use, first decide on what you want your inside diameter of the coil to be, then use a vaping calculator to determine what wire type and gauge you should use to get 7 wraps at your desired resistance. I am not sure why but 7 wraps seems to be the optimum number of wraps (at least to me). Although if building on smaller decks you may not be able to get 7 wraps, so then calculate to get as close as you can to 7. I never go lower than 5 or more than 8 though.
With a mech, in practical terms it's pretty simple. If it feels like you need to turn up the power with a coil, remove a wrap (on the next coil, or however you want to do it). This results in a slightly smaller coil and more power flowing through it. Or vice versa. But for a different experience beyond adjustment, you must a use a different wire (or different numbers of wires, e.g. twisted or different number of coils), either different gauge or material, because otherwise coil size and power flow move in opposite directions, as we just saw. Bigger coils that work well are always lower resistance because it's all interconnected. With a regulated, doesn't have to be like that, you can use the same wire all the time and have your biggest coils be the high resistance ones.
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