Well this post will have it all.
First off let's start off with sizing.
Sizing goes off of waist around and rise.
A general rule is that a small or newborn is 12-13inches by 12 inches or smaller. (8-12lbs)
A Medium is usually 14-16 inches around and 15-16 inches long. (10-20lbs)
A Large is usually 18-19 inches around and 18 inches long. (15-30lbs)
A small/newborn size is easily achieved by getting a newborn prefold.
A Medium usually can be obtained by using your largest prefold.
A large is harder to find because you usually have to buy a toddler sized prefold. I've only been able to find unbleached locally that is long enough to obtain a true Large size. I have not been able to know yet what a true size weight limit would be on these diapers, so the sizes listed are a guesstimate to what I believe they will fit. They could possibly fit more.
So let's get started.
This is how I made a large prefold fitted today.
What you'll need.
Snaps or velcro
Serger(can use a zigzag stitch if you must)
template to cut for diaper
First things first. Cut off the end of the prefold where it was serged and sewn before. You do this to expose the insides of the diaper
Then get your "template" or pattern or just wing it. However you do it, cut out contours for the legs.
Open up and you'll see your diaper is almost ready!
Next comes all the fun parts. You'll start making marks to sew in elastic and sew your extended tabs to your diaper. Your extended tabs will be cut out from the fabric left over from where you cut out the legs. It should be about 2 inches long. This cut out will have a fold from how the prefold was made. This fold is nice because it will leave no seams. You'll lay the folded side of your extended tab over the prior fold from the original prefold. You will stitch this fold to the folded part of your prefold to make the extended tabs. Like this. First pin it.
Sew one side on the folded end, then flip the diaper and sew the other side on the folded end.
And you have extended tabs.
Very gently you'll find the stitching that sews the prefold pad into place. And you'll take your seam ripper and very gently, not to disturb the fragile prefold cloth, you'll take the seams out in the back.
I marked for my snaps
Here again it can get a little tricky. Your snaps need at least 3-4 layers of fabric to be secure. This prefold is a 4x8x4.(4 layers on each side and 8 layers in the middle) You'll need a few extra scraps from leftovers from cutting the prefold earlier.
On my first side, when I peel apart the layers, I find that I have a little overage. From where the pad was sewn in. So I don't need any scraps to secure my snaps. I just put them on.
I peel apart the center pad, dividing them equally and putting my snaps in. 4 layers on the bottom and 4 layers on top where I place my snaps. If I'm careful for placing my snaps I won't need to take out the seams in the pad.
I put a scrap between the layers and carefully put my snaps on. See done!
I carefully pin all my elastic to be cased. You can also zigzag your elastic on if you need to.
So close now I can taste it! I then very carefully and very slowly feed it through my serger.
Then after I'm done serging, I go back through and sew the casings to seal my elastic into place. I'll sew as close to the pad as possible.
For the last step. Mark and place the snaps onto the wing. Or sew the velcro on.
You have just converted a prefold to a fitted.
This may seem long, but the process is actually very quick and easy to sew up. Happy sewing!