First, decide how big you want your napkins. For my everyday napkins, I make them about 15 inches square. That makes it easy as far as figuring - you can get three from about 15 inches of fabric. The width of fabric varies a little so I just measure and divide by three. Depending upon the fabric, sometimes they are only 14.5 inches square. That's fine too. More formal napkins are usually a little larger - maybe 18-20 inches square. At that measurement, you get 4 out of a yard to yard and a quarter of fabric with a strip left over to put in a table runner - see a bonus either way.
Once you have decided and have your fabric cut into squares, it is time to sew. I have a rolled-hem foot for my old machine (okay, I hear you - one of my old machines.) This makes it easy. I just continue one right after the other then snip them apart and move on to side two. You do want your finished edge to be at the bottom of your sewing edge as you work. The unfinished edge is easier to feed into the foot. When you get to the last side, you have to make a little rolled hem and place it under the foot to get it started - at least for this very small one. Some of the rolled-hem feet make a little larger hem, and they seem to be a little easier to feed. If you don't have the presser foot, you can just make a small rolled hem as you would on most sewing projects. I have made hundreds of these, so I love my foot! Now that's something you don't hear every day.
I like to frey check the corners when I am finished just for good measure, but that is entirely optional.
I don't quite have this set finished yet - I'm getting there, but it is really cute fabric so I am enjoying it. Just think, another
excuse reason that is to buy fabric (and help save a tree too.) Have a beautiful day.
As always, Nimble Fingers and Even Stitches.