Help with Sewing measurements?

[Kanti]

Hey guys
I ran into a snag with my tails.
I measured my body exactly every inch or so and divided the total measurement in half so that I would get the two sides of fabric to fit my
entire body rather than two GIANT pieces (obviously).
The measurements were all spot on but I tried the tail on and it's very loose around my waist. I guess the neoprene needs a stretch factor
to account for? The weird part is, it fits great on the bottom where my calves and ankles are, it's just super loose up top.
I decided to add a zipper to make getting in and out easier, but at this point, I have to take 2 inches off each side so I think I'm going to
just drop the zipper (is that a wise choice?).

Is there a specific way to measure a tail so that it fits snug? Do you need to take a few extra inches off so it's tight?
Also, I assume that it won't fall off if I do remove the zipper and just slide it on and off.
I'd appreciate the help, guys, thanks!

[Moonflower]

I think because it's made of a stretchy material you need to make it smaller, depending on the exact give of stretch that the material has. I work with spandex all the time, and you should see how tiny some of the things I make look before they are on the body.
It's the same with elastic - if you need elastic around, say, your ankle to hold spandex leggings down, you wouldn't measure your ankle then cut the same length of elastic, because it wouldn't have any tension when you put it on. Instead, you'd stretch around your ankle so it fits snugly but comfortably and then stretch it out to the spandex ankle part. It will look all weird when off, but lay flat and smooth when it's on your ankle. Make sense?

[Kanti]

Yea, I get it.
I was wondering if anyone knows the stretch factor or not. Maybe there's some sort of % or just a set amount of inches you should shrink it. Especially around the waist, since
that's the part that should be the tightest.

[taom]

Ok so this is what you do (because I totally ran into this problem): Take a piece of tape about the length of your legs and mark every few inches. Put the tape on the side of your leg and take the measurements like normal (at every marked place on the tape). Pull tape off your leg and put it on a big piece of paper. Now, take your measurements and divide them in FOUR. Mark the lengths (that are now one fourth of their former selves) on the paper using the tape as a guide. Then, connect the dots and cut out that side. Fold over, trace, and cut the other side out. It sounds like a lot, but you end up with a very accurate pattern that you can then trace onto fabric. This is how I did mine, anyway.

[Odette]

ALWAYS cut at least one inch more than needed for SEAM ALLOWANCE. very important. bigger is better than smaller. curve your pen/marker/chalk to make it bigger. first hard learned lesson most people make. tails are such a confusing sewing project.made a dress once and was too small and too big in areas cuz of this. =/

[Taylor is a Mermaid]

I honestly think that making the pattern/getting it to fit right is the hardest part of the whole process. Harder than the scales, harder than sewing spandex (haven't tried neoprene yet), harder than painting the fluke and even harder than sewing the very fussy frill on mine. This is the thing I dread when I think about helping a friend make another tail. What I ended up doing was just taking it in after it was sewn, because I couldn't get the measurements to come out right. I know that's not the best solution, but I had already remade the pattern once and I was just not getting it.