You can adjust the measurements and the type of fabric. I used a colorful canvas type because I was looking for durability. The color hides dirt. The canvas should resist tears for quite a while. I am a bit rough on my bags--they go everywhere with me and I am as likely as not to throw them on the floor in a corner just to get them out of the way. You could easily use a pretty or lacy fabric but then I would take the time to line the bag.
The cording I used for this project came from a braiding technique I learned from an instructable that was demonstrating how to make friendship bracelets. (Braiding Wheel Friendship Bracelets by sherrycayheyhey)
Step 1: Materials:
thread--matching or contrasting
Sewing machine or just a needle
Cording for the shoulder strap
Hook and loop, button or snap closure
Step 2: Cutting the Fabric
Cut 2 rectangles. Cut each piece the same size. Make the width 3 inches wider than the finished width. Make the height 2 inches taller than the maximum height you want for the bag. The extra fabric will allow you to turn under the edges so the fabric does not fray.
If you are lining the bag, you can cut the lining an inch and a half less wide and an inch less high.
I planned to use my bag for carrying my wallet sized purse, my tablet, a sewing project, a snack (or 2), and anything else I might need when I am off to the doctor's office, my mother-in-law's hair appointment, or a robotics competition. It is kind of a grown up version of a diaper bag. It has to hold everything I need to survive a day.
Step 3: Hem the Top and Bottom
You can do all the sewing using a sewing machine but this is too small of a project for me to bother getting it out. I sew so much by hand that I am probably faster with a needle and thread anyway. Fold the top edge over 1/2 inch and then fold it over another 1/2 inch again. You can iron the first fold and then fold it the second time--depending on your fabric choice this could make things easier. I usually find that pinning the fabric works well for me.
Stitch the fold in place. I like the look of top stitching and usually use a contrasting color of thread because I want it to show.
The purpose of this is to hide the raw edge of the fabric on the inside where it will not fray. If your fabric does not have a fraying problem, you can probably get away with only one fold. I would still put in at least the single fold--you want the extra durability.
Repeat the double fold and stitching line for the bottom edge.
If you are lining your bag, the lining layer edge should be caught inside the fold of the outer fabric.
Step 4: Side Seams
Fold the side edges in 1/2 inch on each side. Fold over a second time but make this fold an inch. Pin or iron--which ever worked best for you. Lay the 2 pieces on top of each other with the outside of the fabric facing out. Line them up carefully and pin the sides. Sew from top to bottom just under an inch (7/8 inch) from the edge. This creates a channel for the shoulder strap. For a bit of extra strength, I sew a second line of stitches. Next to the first row at 3/4 inch from the folded edge. Do this on both the left and right edges.
Step 5: Bottom Seam
Be careful on this step to leave the channels you just made open. This is probably easier if you are hand sewing but I have done it once or twice on a sewing machine.
Open the bag and layer the 2 bottom edges. Sew through both the pieces of fabric creating a sturdy bottom edge. Again, I usually sew 2 lines of stitches.
Step 6: Strap
Cut 2 pieces of the cording. To figure it how long to make each piece you will have to measure from where you want the bottom of the bag to end up when you are carrying it up to your shoulder. Double this and add an extra inch or 2. (It is better to have an extra inch than to end up just a bit too shout.) Cut both pieces the same length.
Thread one piece of the cord up the left side of the bag and then down the right side of the bag. Do the same with the other cord in the second set of channels. All the cord ends should be at the bottom of the bag.
Tie the 2 cords on the left side together. Tie the 2 cords on the right sides together.
The bag is now usable. Sometimes when I make this bag, I stop here. The closure at the top edge is not always necessary--it kind of depends on how you will be using the bag. Mine is going to be a large purse--it needs a closure. I have a few that are more like reusable shopping bags and I rarely use the closure on them.
Step 7: Closure
I like to use hook and loop tape for bag closures but you can use whatever you have on hand. Sew your closure device(s) near the top edge. For a small bag, you may need only one closure. A larger bag may need 2 or 3.
If there is only a little in the bag, you can slouch it down. Stretch it taller as you stuff more in it.