What has an influence on weighting?
1/ Your physiology (weight) and your body mass index (weight/size).
2/ Water: buoyancy is greater in seawater (you need more weights) than in fresh water.
3/ Your diving suit: the thickness of the neoprene also influences buoyancy.
4/ The weight of the tank (for SCUBA diving) and the volume of the air content: the more air you consume, the lighter your cylinder becomes and your buoyancy tends to become positive (you float!).