I followed the guide to measure my foot, it fit into both M and L so I chose the smaller ones thinking it would be more beneficial. They are too small. The returns process has been very good so far, with immediate responses to emails and hassle free send it back in same bag so no costs to me. Very happy with service thus far. Would recommend if you have a broad foot going up a size if you fit into two sizing categories. As far as the sock the relief from plantar fasciitis pain has been incredible. I kept one small pair as had already tried on and been wearing to see if it was comfy enough that tight,