Baby Food Pincushions

If you use a jar with a differently sized lid than the one used in the tutorial, the formula for cutting the right sized fabric circle for the top is:

The radius of the circle needs to be one jar-lid width plus seam allowance.

To accomplish this, I cut a strip of cardboard and I pin through one end (point A) of it to be the pivot point at the center of my circle. From that pin I measure along the cardboard strip at the widest part of my jar lid and make another pin hole (Point B). I add another 1/4 or 1/2 inch for the seam allowance and make a third pin hole (Point C). If the fabric is loosely woven or inclined to fray then I use a wider seam allowance.

Enlarge points B and C until you can slip the point of a drawing implement through the hole -- I like to use Berol Prismacolor colored pencils, personally. Pin through the hole at Point A, and through the fabric you are using at the point that will be the center of your circle, and into a support that is large enough to draw the circle, firm enough and smooth enough to let you trace a good line, and soft enough that you can pin into it far enough to get some stability. (I often use a layer of stiff cardboard covered with a thin stack of junk-mail so that the cardboard corrugation doesn't irritate me.) You'll be pinning through these layers by inserting the pin straight down so that the cardboard strip can pivot smoothly around it. Trace one arc all the way around at Point B for your sewing line and a second arc all the way around at Point C for your cutting line. :)