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Multiply length × width × height in inches, divide by 231 for US gallons. Subtract 10–15% for substrate, rocks, and driftwood displacement.
Gallons = (L × W × H) / 231; Liters = Gallons × 3.785Bow-front tanks have a curved front panel adding volume beyond a rectangular estimate. Use the manufacturer's stated volume or add 8–12% to rectangular calculation.
Bow-front volume ≈ Rectangular volume × 1.10Calculate circular cross-section area times height. Cylinder tanks and bowls require diameter (not radius) for the base area calculation.
Gallons = (π × (D/2)² × H) / 231Updated: July 2026
48 × 13 × 21 / 231 = 56.6 gallons nominal. With 2 inches of substrate and hardscape, actual water volume is ~48–50 gallons — use this for dosing and stocking.
Rectangular estimate from 30×15×21 gives ~43 gallons. Bow curve adds volume; manufacturer rates at 36 gallons. Trust manufacturer spec for bow-front and irregular shapes.
π × 10² × 24 / 231 = 32.6 gallons. Tall narrow tanks have less surface area for gas exchange despite decent volume — factor into stocking decisions.
Glass thickness reduces internal dimensions by 1–1.5 inches per dimension on large tanks. Always measure inside the glass for accurate volume.
Medication overdosing from using 55 gallons instead of actual 48 gallons can harm or kill fish. Calculate actual water volume after substrate and hardscape displacement.
Accurate tank volume is essential for dosing medications, calculating filter capacity, and stocking limits. This calculator computes water volume in gallons and liters for standard rectangular, bow-front, cylinder, and corner aquariums, accounting for substrate depth and hardscape displacement.