Aquarium volume calculator: net gallons, weight and heater

Gross and net volume of a rectangular, cylinder, corner or bow front tank, minus glass, substrate and decor, in liters and US gallons, with filled weight.

Aquarium volume: gross liters, net liters and filled weight

Gross volume = outside length × width × height ÷ 1,000 (cm³ to liters). Net volume removes the glass thickness on every wall and the bottom, the unfilled height, the substrate and the decor: a tank sold as 200 L holds about 150 L of water.

Method

  • Inside: each wall moves in by the glass thickness e, the bottom too; the inside height is H − e.
  • Corner tank: a quarter circle of radius R with the right angle against the wall. Bow front: a circular arc with chord L and bow depth B, the inner face having radius r − e.
  • Net water = inside area × (water height − substrate) − decor volume.
  • Weight: glass at 2.5 kg/L (2,500 kg/m³), water at 1 kg/L, substrate at its bulk density.

Example

A 100 × 40 × 50 cm tank in 8 mm glass: 200 L gross. Inside 98.4 × 38.4 × 49.2 cm = 185.9 L. With 3 cm below the rim, 5 cm of sand (18.9 L) and 5 L of decor, 150.7 L of water remain, or 39.8 US gallons. The glass is 14.1 L, so 35.2 kg; with sand at 1.6 kg/L (30.2 kg), the total is 216 kg, about 476 lb, without stand or decor.

Limits

Sand is counted as solid although water fills its gaps, so actual water is slightly higher. Sand density (1.6 kg/L), heater power (1 W per liter) and filter turnover (4 times the volume per hour) are indicative values, not verified against an official source: adjust them to the maker's advice. No stocking advice is given.

Sources and dates: NIST Handbook 44, Appendix C (US gallon = 231 in³ = 3.785411784 L); AGC, Planibel technical data sheet 11/2024 (EN 572-1 glass, 2,500 kg/m³) (checked on 29/10/2026)

Frequently Asked Questions

How do I calculate aquarium volume in gallons?

Multiply length × width × height in inches and divide by 231, the cubic inches in one US gallon. In centimeters, divide by 1,000 for liters, then by 3.785 for gallons: 100 × 40 × 50 cm is 200 L, or 52.8 gallons gross.

Why does my tank hold less water than its size?

Glass, the gap below the rim, substrate and decor all take space. A 200 L tank in 8 mm glass with 3 cm below the rim, 5 cm of sand and 5 L of decor holds about 150 L, or 39.8 gallons.

How much does a filled aquarium weigh?

Count 1 kg per liter of water (8.3 lb per gallon), 2.5 kg per liter of glass and the weight of the substrate. The 100 × 40 × 50 cm example weighs about 216 kg, or 476 lb, without the stand.

How is the volume of a bow front tank calculated?

The front is a circular arc: floor area = rectangle + circular segment with chord L and bow depth B, then × height. A 100 × 40 × 50 cm tank with a 15 cm bow is about 251 L gross.

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