Total weight is a useful starting number, but support safety depends on where and how that load is transferred.
Water, glass, stand, substrate, rock, sump water and equipment all contribute. A realistic component total is the first useful number.
A broad cabinet, four small feet and a pedestal stand distribute weight differently even when total mass is identical.
Original diagram supporting the aquarium load planning basics explanation.
Concrete slabs, suspended timber floors and upper-storey joist systems behave differently. Span and joist direction can matter in timber construction.
A generic website cannot see the floor, inspect fixings or know whether alterations have been made. It can help you estimate mass but not certify structural adequacy.
For large installations or uncertain structures, suitable structural advice is more appropriate than a simplified internet rule.
The arithmetic starts with a total mass estimate. The structural question is how that mass reaches the floor: over what footprint, through what stand, at what position in the room, and over what type of floor construction. Those details are outside the scope of a generic web calculator.
Use the weight tool to avoid under-counting the installation, then seek appropriate structural advice when a large aquarium, unusual floor or uncertain building construction makes the answer important.