probably semantics to cal the one fin-tube, the other baseboard. n the end the overall capacity is important. Capacity depens on fin-size, fin-spacing and wtater temp and the manufacturer can give you that.
Careful, they lose capacity quick with low water temp. They really are not good if you actually need lot of heat.
And there is a tube velocity component that affects heat transfer. Not near of a factor as temperature, but it is there. Thus an over sized tube may... just may kick out less heat than a smaller diameter or correctly sized tube w/ higher velocity. As other two posts, surface area, fin size/spacing all is important. Need to consult mfgrs tables, most setup for 3 ft/s
