I based this pattern on a reusable shopping bag I bought at Wal-mart. It seems to be a little bigger than the bag that comes from Publix, our local chain grocery store. You might want to take a peek at the bags that come from your local store to see what size they are. Otherwise, start with just one bag, and take it to your local grocery to see how it works. My local Wal-mart cashier was concerned that the handles might not fit over the metal brackets that hold the bags open for filling. They turned out to be fine, but it is worth checking into before you make 20 bags that don't work well at your local market.
Step 1: Choosing the Fabric.
You will need fabric that is somewhat sturdy. I used leftover home decorator fabric. Indoor/Outdoor fabric, canvas or denim would also be good choices. You will need about 1/2 of a yard per bag. 17 inches to be exact, but 1/2 a yard should give you insurance for raveling edges and such. This is assuming you are using home decor fabric which is at least 53 inches wide. If your fabric is 45 inches wide, you will need 3/4 of a yard.
Step 2: Cutting the Fabric.
You will need 5 pieces of fabric total. Piece A forms the front, bottom and back of the bag. It is 14 inches wide by 36 inches long. Piece B forms the two sides of the bag. They are both 14 by 8.5 inches. You should be able to get all three these from a single 14 inch cut. If you are using 45 inch fabric, you will need to cut a second piece at 8.5 inches in order to get both side pieces. Piece C forms the handles. They are 3 inches by 23 inches. Again, both of these should come from the same strip of fabric. Your handles will be slightly shorter if you are using 45 inch fabric, just cut it in half and it will be close enough.
Step 3: Preparing the Handles.
Take a handle piece C. Laying it flat with the wrong side up, bring both sides to the middle and crease to form a tube with the right sides out. You may iron it flat if you like. Use a zig zag stitch straight down the middle to hold the two sides together and cover the raw edges. If you overlap the edges slightly, it make is harder to miss if you sew a little crooked. Repeat for the second handle.
Step 4: Connecting the First End.
This is the tricky step. You want to connect three sides of piece B to piece A. This needs to be done in one continuous seam. In order to accomplish this, you will need to pivot at each corner using a needle down position.
Start by laying piece B at the top right hand corner of piece A. With right sides together, sew straight down the side, stopping one seam allowance short of the end. Stop and needle down if your machine does not do this automatically.
While the needle is down, readjust the fabric, bringing the bottom of the side piece over to meet the edge of piece A. Depending on how stiff your fabric is, you may need to fiddle with the corner, or even cut a little divot in order to allow the fabric to turn the corner. Continue to sew down the bottom side, stopping one seam allowance short of the end. Pivot again, and sew to the end of the third side.
You will have a U shaped tube connected to one side of the bag. The top of the bag may not be even on the last side you sewed, depending on what seam allowance you used. I used a quarter inch, and this made the end of piece A about half an inch too long on the end. If you knew ahead of time exactly what seam allowance you wanted to use, you could make your piece A shorter by one seam allowance and it should turn out perfect. I like to adjust my seam allowance depending on the fabric I'm using, so I prefer to leave piece A a little long and trim it after I sew on the first side piece. When you get to the end, just trim off whatever is left so that the edges are nice and even.
Step 5: Connecting the Second Side
Side two goes on exactly the same as side one. When you are done with both side pieces, you'll have a 5 sided rectangular shape that is open on the top.
Optional Step 6: Finishing the Edges
If your fabric seems likely to fray, or if you think you might be washing your bag quite a bit, you might want to finish the raw edges. Just keep the bag wrong side out and zig zag over the edges. This is assuming you don't have a fancy serger machine, which I don't.
Step 7: Finishing the Top and Attaching the Handles.
Keeping the bag wrong side out, fold the top down so that you have about one inch of overlap all around. I pin this step, it helps to hold everything together. After the top is pinned, lay it out flat and pin the handles down, about 2.5 inches from each side. Make sure the bottom of the handles are even with the bottom of the top hem.
Now carry the whole thing to the sewing machine. Starting at a corner and using a zig zag stitch, sew along the bottom of the hem, covering the raw edges, and connecting the handles at the same time.
When you get back to where you started, stop and needle down. Switch to a straight stitch and pivot the bag, sew straight up the corner, stopping near the top of the bag. Needle down and pivot again, just below the top edge of the bag. Sew around the bag again just below the top edge, securing the handles and finishing the top edge.Turn your bag right side out and poke out the corners. Pleat the bottom so that it will fold flat, and tuck the handles inside for storage. You should be able to store quite a few of them in a very small amount of space. Stash them in your car so they are handy for your next unexpected trip to the grocery store!