I have 18” calves but small feet (5’8” tall), so I’ve gone through a lot of different compression stockings before finding these. Combined with socks for plantar fasciitis, they really work to keep the swelling down and my feet/legs pain-free!
Since I was right on the border of L and XL, I ordered a size each. I like the tighter compression feel of the L, but both sizes worked well in keeping my swelling down. I’d say if you are right on the edge of 2 sizes and like a tighter feel, go with the smaller size for your calf measurement.
I’m going to order several more pairs of these-they also are keeping shape/compression after a few times through the washer/dryer.