This tutorial is part of the “Build a Zip Pouch Series“, giving you the skills you need to sew custom zip pouches in a variety of styles and sizes. Links will be added to the series homepage (here!) as new tutorials go live.
If the contents of your pouch are on the slim side or you’re looking to keep things simple, you won’t need this step to add depth. Instead, you’ll finish with the standard 90 degree corners or rounded ones.
If you do want depth to your pouch, you’ll need to adjust the cut dimensions accordingly or be okay with a slightly smaller zip pouch in height and width. For a great, thorough, description of how to calculate depth with boxed bottom corners, check out this post (you need to scroll down a bit to get to the actual tutorial). I’ll cover the basics and my favorite method below.
Figuring Out Cut Dimensions
When you box a bottom corner of your zip pouch, you’ll be taking away some of the height and width of the pouch in the process. For example, if you sew a 1″ wide boxed corner, you’ll create 1″ in depth for your pouch. Doing this will cause the bottom of your pouch to be 1″ shorter in width and 1/2″ shorter in height. Account for this difference in your cut measurements by adding 1/2″ in height to each lining and exterior piece and 1″ in width.
Note: With larger boxed bottoms, there will be a noticeable difference between the length of the zipper top and the length of the bottom. It’s not as noticeable on smaller sized boxed bottoms (1″ or less). If you’d like to have the bottom and the top of the pouch be exactly the same length, while still adding depth, just add the extra width to the bottom of the pattern piece you’re making, then draw a diagonal line from the shorter top edge to the longer bottom edge.
Cutting the Corners
To prepare your fabric for boxed corners, place each lining and exterior piece on your cutting surface. You can do this after inserting the zipper (as I did in the example below) or before. You will be cutting the squares out of the bottom two corners of each exterior and lining piece.
The width and height of the square cutout needs to be one half of the depth you desire.
Sticking with our 1″ boxed corner example, I cut 1/2″ x 1/2″ squares out of the bottom corners of each fabric piece of my pencil pouch.
Sewing the Corners
Before sewing the boxed corners, sew around the rest of the pouch with a 1/4″ seam allowance. After the side, top, and bottom seams have been sewn (make sure to still leave a turning hole in the bottom!), you’ll move on to sewing the four boxed corners.
Pinch the cut corners (one pinch on the lining side and one pinch on the exterior side). Pull the two corners away from each other so the right sides lay flat together, forming a straight line. Line up the side and bottom seams, nesting them (have the seams laying in opposite directions). Clip or pin in place then sew using the same seam allowance you used for the rest of the pouch.
Repeat with the other three corners before trimming seams and turning the pouch right side out.
To figure out the cut measurements for a custom sized zip pouch with a boxed bottom use the following: Add half of the desired depth (boxed bottom) to the height of each cut piece. Add the entire desired depth (boxed bottom) to the width of each cut piece.
To figure out how a boxed bottom will alter the dimensions of already cut fabric: Subtract half of the desired depth (boxed bottom) from the height of the zip pouch. Subtract the entire desired depth (boxed bottom) from the width of the zip pouch.