40 Gallon Breeder Tank: Dimensions, Volume & Weight
A standard 40 Gallon Breeder aquarium measures about 36 x 18 x 16 in (91.4 x 45.7 x 40.6 cm) and holds 151.4 L (40 US gal) at its full nominal rating. At a typical 90% fill with 15 L of substrate and decor, usable water volume is about 121.3 L (32 US gal); filled, the water alone weighs about 333.1 lb (150.9 kg). Figures use the exact 1 US gal = 3.785411784 L conversion and published standard external dimensions, compiled 2026-09-25.
- Nominal size
- 40 US gal
- Standard footprint
- 36×18×16 in
- Nominal volume
- 151.4 L
- Usable volume (90% fill)
- 121.3 L / 32 gal
- Full tank water weight
- 333.1 lb / 150.9 kg
| Fill level | Usable volume (L) | Usable volume (US gal) |
|---|---|---|
| 80% | 106.1 | 28 |
| 90% | 121.3 | 32 |
| 100% | 136.4 | 36 |
Open this size in the calculator
Dimensions, weight, and fill assumptions
These are typical external footprint dimensions published across major US tank manufacturers' standard-size charts, not a measurement of one specific tank on a shelf; rimless, low-iron, and non-US models can differ by an inch or more per side. The nominal 40 US gal rating is the manufacturer's full-tank figure, so it slightly overstates the water you will actually keep: after subtracting a typical 15 L (about 4 US gal) of substrate, decor, and hardscape, and filling to a realistic 90% of the rim height to leave room for equipment and evaporation, usable volume drops to 121.3 L. Water weight uses fresh water at about 25 degrees C (0.997 kg/L, 8.328 lb/US gal); a filled tank also carries the glass, stand, substrate, and hardscape, so total load on a floor or stand is higher than the water weight alone. The prefilled link below opens TankStockPlan with this size's typical external dimensions, a 90% fill, and 15 L of displacement already entered; replace the length, width, and height with your own internal (inside-the-glass) measurements for an exact usable-volume figure, since that is what actually determines how much water and livestock the tank can support. Prioritize animal welfare. A specialist-reviewed husbandry plan and a properly cycled, stable aquarium are required; this calculator is not approval to add fish.