You will need:
Fabric for the shell of the belt (can be two different colours; then it's reversible!)
Fabric for interlining (you may omit this if your shell fabric is heavy and stiff)
Ultra-stiff sew-in interfacing/stabilizer (you may omit this if you don't need your belt to bear weight)
Something to secure your belt - a clasp, a large D-ring, etc.
Optional: 1-inch D-rings
If you are going to use a normal belt buckle, you will also need:
A leather punch
A belt buckle of the appropriate width
Note: If you buy things from Jo-Ann Fabrics, always use the coupons! I never pay full price there.
Plus normal sewing things: thread, scissors, pins, measuring tape or ruler, pen/pencil/chalk, etc.
For inserting the interfacing, you will also need a hand-sewing needle and a cork, rubber eraser, or similar item.
Step 1: Cutting the Fabric
If you are tapering one (or more) end, as I am doing, sketch the taper shape on the wrong side of the fabric with a coloured pencil or chalk. To ensure it is symmetrical, just sketch one half of it on the fold. Also sketch 1/2" in from your cut line, to ensure it will look right after taking into account seam allowances. Fold your fabric in half lengthwise, then trim your shape.
Cut a second strip of your shell fabric, and two strips of your interlining (if you're using it). If you've tapered one end, it is helpful to trace your original strip to ensure an exact match. I also like to trace a mark at each end of the long straight sides, and then use a yardstick to get a perfectly straight line.
Stitch each interlining piece to the wrong side of a shell piece, with a smaller seam allowance than normal. Since we're using a 1/2" seam allowance for the rest of the sewing, we use a 3/8" seam allowance for this step. This ensures the stitching from this step will be fully hidden within the final seam allowances. Trim the interlining a bit.