This is an easy reconstruction to make too small jeans bigger and punk them up at the same time.
All you have to do is measure the fullest part of your lower body and divide it by 2. Example: 42 inches around fullest part of hips divided by 2 = 21 inches.
You then lie the jeans flat and do a measurement at the fullest part of the hips. Example: 17 inches
You then subtract the difference between your measurements and the flat measurement of the jeans, divide that by 2 then add in what ever you want to allow for seam allowances and times that by 2. I used 1/2 in seam allowances so I added 1 inch.
Fullest part of hips: 21
Flat measurement jeans: 17
Difference = 5 in
1/2 in x 2 = 1 in
Total width each side. 6
For the length, measure the full length of the pants
Example: 40 inches
1 1/2 inch (for the top to add the elastic and the bottom for the hem)x 2 = 3 in
Length of jeans = 40 in.
Top & bottom hem 3 in.
Total length: 43
In this case, you would want to cut 2 strips that is 6 in wide and 43 in long. (I used around 1 1/2 yds of funky red alligator look polyester fabric that I had gotten at Walmart for $1 a yd. and had plenty left over for other projects).
I folded the top and bottom of each strip and sewed around 1 in for each edge. On the top part, I added around 3 inches of elastic (I used 5/8 in pre-packaged elastic that I got from Walmart for less than $1, sewed it down on one side then pulled it through and sewed it down on the other side, then sewed each strip (right sides together on fabric and jeans)and it was done.