40 gallon long fish tank: dimensions, weight & setup
A standard 40 gallon long tank measures 48 × 12 × 16 inches, holds about 34.9 gallons of real water and weighs roughly 390 lb once set up. It is a great size for active schooling fish that need length more than depth.
40 Gallon Long tank dimensions
| Inches | Centimeters | |
|---|---|---|
| Length | 48 in | 121.9 cm |
| Width (front to back) | 12 in | 30.5 cm |
| Height | 16 in | 40.6 cm |
| Footprint | 576 in² (4.0 ft²) | 3,716 cm² |
| Typical glass | 1/4 in | 6 mm |
These are typical outside dimensions for US glass tanks; brands vary slightly, so measure yours before buying a stand, lid or background.
How much water does it really hold?
| US gallons | Liters | |
|---|---|---|
| Outside dimensions | 39.9 | 151.0 |
| Filled 1 in below the rim | 34.9 | 132.0 |
| With 2 in of gravel | 30.2 | 114.1 |
Dose medication and fertilizer for the real water — about 30 gallons once the tank is aquascaped, not 40.
How much does a 40 gallon long tank weigh?
| Empty (estimated, 1/4 in glass) | 62 lb | 28 kg |
|---|---|---|
| Filled with fresh water | 353 lb | 160 kg |
| Set up, fresh water + 2 in gravel | 391 lb | 177 kg |
| Set up as saltwater | 397 lb | 180 kg |
| Floor load under the stand | 98 lb/ft² | 4.7 kPa |
Add rock, decor and the stand (often 40–120 lb). A floor load of 98 lb/ft² is 2.4× the 40 lb/ft² a typical home floor is designed for when averaged over a room, so place the stand across the joists and near a load-bearing wall. Use the weight calculator to include your own rock and stand.
Heater size
| Room temperature (water at 78 °F) | Heater |
|---|---|
| 73 °F (5 °F lift) | 75 W |
| 68 °F (10 °F lift) | 150 W |
| 63 °F (15 °F lift) | 200 W |
Colder room, nano heater or dual-heater setup? See the 40 gallon heater size chart.
Plan maintenance with the water change schedule: a 30% change on this tank is about 9.0 gallons.
Filter flow
| Tank type | Real flow | Filter rating |
|---|---|---|
| Community tropical | 140–209 GPH | 199–299 GPH |
| Planted tank | 174–279 GPH | 249–399 GPH |
| Goldfish, cichlids or heavy feeders | 279–349 GPH | 399–498 GPH |
Substrate
| Depth | Gravel | Sand |
|---|---|---|
| 1 in (2.5 cm) | 32 lb | 31 lb |
| 2 in (5.1 cm) | 63 lb | 61 lb |
| 3 in (7.6 cm) | 95 lb | 92 lb |
Stocking ideas
- 10 zebra danios + 8 cherry barbs + 6 corydoras
- 12 harlequin rasboras + 6 kuhli loaches + 1 bristlenose pleco
- 8 tiger barbs (species-only to avoid fin nipping) + 6 corydoras
Check any combination — including temperature and group size — in the stocking calculator.
Setup tips
- Four feet of length gives fast swimmers like danios and barbs a real run.
- The 12-inch depth limits aquascaping depth; use height and the back glass for visual depth.
- Uses the same 48-inch lights and hoods as a 55-gallon.
← 40 gallon breeder55 gallon →
FAQ
What are the dimensions of a 40 gallon long fish tank?
A standard 40 gallon long glass tank measures 48 × 12 × 16 inches (121.9 × 30.5 × 40.6 cm) on the outside, a footprint of 4.0 square feet. Brands differ by up to about half an inch.
How much does a 40 gallon long fish tank weigh?
About 60 lb empty, 355 lb filled with water and roughly 390 lb set up with 2 inches of gravel, before rock, decor and the stand.
How many gallons does a 40 gallon long tank really hold?
39.9 gallons by its outside dimensions, about 34.9 gallons (132 liters) filled an inch below the rim, and about 30.2 gallons with 2 inches of gravel.
What size heater does a 40 gallon long tank need?
150 W to hold 78 °F in a 68 °F room; 75 W in a 73 °F room and 200 W in a 63 °F room.
How much gravel or sand for a 40 gallon long tank?
About 32 lb of gravel per inch of depth: 63 lb for a 2-inch bed, or 61 lb of sand.
What filter flow does a 40 gallon long tank need?
140–209 GPH of real flow for a community tank (4–6× turnover), so choose a filter rated about 199–299 GPH.