Build a component load ledger instead of stopping at the weight of the water.
For rough freshwater planning, one litre of water is close to one kilogram. A 200-litre setup can nevertheless weigh far more than 200 kg once the glass, cabinet, substrate and rock are included.
List water, empty tank, substrate, rocks, wood, external-filter or sump water, equipment, cabinet and anything stored permanently below the tank. Use manufacturer weights where available.
Original diagram supporting the how much does a full aquarium weigh? explanation.
A setup with 180 litres of water, a 30 kg tank, 25 kg of substrate and rock and a 35 kg stand is already about 270 kg. That is the kind of total that matters for handling and support planning.
Structural safety depends on how the load is transferred, not just the total mass. Stand feet, cabinet design, floor construction, joist direction and span are outside the scope of a simple calculator.
If there is any doubt about the supporting structure, seek suitable structural advice instead of treating an online arithmetic result as approval.
Water litres are only the first line of the calculation. Add the tank, cabinet, substrate, hardscape and equipment as separate entries. That makes the estimate auditable and easy to update if the setup changes.