How to size an aquarium
Size to the animal, with growth headroom
A common starting rule is 1 inch of fish per gallon, but that under-counts for active or large fish. Better: pick by adult-size of the species you're keeping, not the size at purchase. Beginner setups: 20–29 gal (24″×12″×16″). Community tanks: 40–75 gal. Large species or schools: 90+ gal.
Floor and weight load
A filled aquarium weighs roughly 10 lb per gallon — a 75 gal tank weighs 750 lb when full, plus the stand and equipment. Check floor-load ratings: most US residential floors handle 40 lb/sq ft live load, which constrains tanks above 75 gal in upstairs rooms. Older homes and elevated floors need the tank placed perpendicular to floor joists, ideally over a load-bearing wall.
Placement and access
Allow access on all sides you'll need to reach — cleaning, feeding, and routine maintenance. Cabinets that look fine empty become impossible to use when crowded against a wall.
Common mistakes
- Sizing by current animal/setup rather than the long-run plan.
- Skipping the floor-load check on upper storeys or older buildings.
- Forgetting access — the back wall is part of the maintenance plan, not just decor.