Equivalent to standard shoe size. Light. I've worn them in the sea and the sole was thick enough to protect my feet from sharp projectiles etc. The adjustable straps are great and they never slipped off. I clicked in too and nothing hit them, not even sand. Comfortable to wear out of the water as well - they are supportive, unlike the basic/cheap water shoes which have in the past caused my arches to hurt when walking on dry land. Definitely recommend.