How aquarium volume calculator Works
Real gallons vs box gallons
Every gallon claim assumes an empty glass box: substrate, rocks, wood, and equipment displace 10–25% of it. A "planted" 20-gallon holds ~16 real gallons — and stocking math, medication doses, and water-change percentages all run on the real number. The calculator subtracts honestly.
The weight is the real question
Water weighs 8.34 lb/gallon: a 55-gallon tank is 450+ lb filled before the stand counts. Floors have limits (a 75-gallon on an interior wall is fine; on a second-floor overhang, check joists), and cheap stands fail expensively. The filled-weight line is the calculator's most-skipped and most-important row.
Footprint beats height
Fish live in surface area more than volume: a long 20-gallon (30×12) stocks better than a tall 20 (24×12) at the same height of water — oxygen exchange and swimming room run horizontal. Tall tanks suit angelfish and décor; long tanks suit everything else.