I am often asked if my stitch markers are heavy or if they will pull on the stitches? The average stitch marker set weighs less than an ounce. They do not pull on your stitches because they rest on the needles not the yarn or stitches. Of coarse if you are working on a large project like an afghan and you are using like 50 stitch markers your project will be a bit heavier than without stitch markers. I know some knitters have to be extremely careful because of arthritis and other problems from over knitting but I try to keep this in mind when creating stitch markers and choosing light weight beads.
Another lighter weight option if this is a concern is my wire loop markers. In these I use beading wire in place of the rings. The wire is flexible and thinner than the rings.
If you are concerned about the weight of a set please contact me so I can help you choose the best possible options for your needs.