Fish Tank Volume Calculator

Free fish tank volume calculator for 6 shapes. US gallons (231 cu in each), liters, UK gallons, water weight at 8.34 lb/gal, plus heater sizing.

Fish Tank Volume Calculator

Tank Shape

Units

Length (in)

Width (in)

Water Height (in)

Fill Level (%)

US Gallons

51.1 gal

Liters

193 L

UK Gallons

42.5 gal

Water Weight

426 lb (193 kg)

Heater Size (3-5 W/gal)

153-255 W

Loaded Weight (≈10 lb/gal rule)

≈567 lb

ℹ️ Measure inside the glass and use actual water height (below the trim) for true volume — substrate and decor displace more. A “55 gallon” typically holds about 48 usable gallons.