The 40 gallon breeder and the 55 gallon are two of the most popular mid-size aquariums. Surprisingly, the smaller tank has the bigger footprint. The right choice depends on what you want to keep and how you want it to look.
40 breeder vs 55 gallon at a glance
| 40 gallon breeder | 55 gallon | |
|---|---|---|
| Dimensions (L x W x H) | 36 x 18 x 16 in | 48 x 13 x 21 in |
| Footprint | 648 sq in (4.5 sq ft) | 624 sq in (4.3 sq ft) |
| Volume | 40 gal (151 L) | 55 gal (208 L) |
| Full weight with 2 in gravel | about 467 lb | about 609 lb |
| Gravel for 2 in bed | about 75 lb | about 72 lb |
| Heater | 200 W | 250 W |
| Filter flow | 160–240 GPH | 220–330 GPH |
Typical standard sizes; brands vary slightly. Weights assume fresh water and the empty glass weight listed on each tank page.
Why the 40 breeder is so popular
- Depth for aquascaping. 18 inches front to back leaves room for foreground, midground and background planting.
- More floor for bottom dwellers. Corydoras, loaches and dwarf cichlids use floor space, not height.
- Easy to light and reach. At 16 inches tall, light reaches the substrate and your arm reaches the bottom.
- Lighter. About 140 lb less when full, and it fits common 36 inch stands.
Why choose the 55 gallon
- More water. About 15 gallons more, which keeps temperature and water quality steadier.
- Swimming length. At 4 feet long, it suits active schooling fish such as rainbowfish and danios.
- Height for tall fish. Angelfish and tall plants appreciate the 21 inches.
- Upgrade path. Its 48 inch length matches many 4 foot lights and stands.
The trade-off: at 13 inches deep, the 55 can look like a narrow corridor, and aquascapes have less room for depth.
Which should you buy?
Choose the 40 breeder for planted tanks, bottom dwellers, dwarf cichlids and shrimp, or if weight and reach matter. Choose the 55 gallon for long-bodied or fast schooling fish, angelfish, and if you want the extra water volume. If you can fit a 4 foot tank and want the best of both, look at the 75 gallon: the same 48 inch length with an 18 inch depth.
Planning the setup? Use the substrate calculator and see the heater size guide.
Frequently asked questions
Is a 40 breeder bigger than a 55 gallon?
Not in volume: the 55 holds about 15 gallons more. But the 40 breeder has a slightly larger footprint, 648 square inches against 624, because it is 18 inches deep instead of 13.
Which is better for a planted tank, 40 breeder or 55?
The 40 breeder usually suits planted tanks and aquascapes better. Its 18 inch depth gives room for a sense of depth, and its 16 inch height lets light reach the substrate.
Which is better for angelfish?
The 55 gallon. Angelfish grow tall, and the 55's 21 inch height and 4 foot length suit a group better than the 40 breeder's 16 inches.