There were a variety of maces in the Middle Ages. They differed in shape of the head (Studded Mace, Flanged Mace, Indian Shishpar), in metals used (wood, copper, bronze, iron), and in length (cavalry usually had longer maces) all of which would determine the final mace weight.
Most of its weight is concentrated at the end, which made this Medieval Weapon rather unbalanced and hard to master. But it was still popular weapon as it was cheap and easy to produce.
They were mainly used by the cavalry and knights as it was very effective against armored opponents (much more effective than bladed weapons like sword or dagger, as these could not make much harm on the Medieval Armor). A strong blow from a mace could penetrate even thick armor.
Various maces weighted differently, but usually they were around 1kg – 1.5kg. A two-handed sword like longsword could weigh even more than that, so Medieval Mace did not weigh that much when you think about it. During battle, they were used in one hand, but bigger and heavier two-handed maces were also available in the Medieval Times.