20 gallon long fish tank: dimensions, weight & setup
A standard 20 gallon long tank measures 30 × 12 × 12 inches, holds about 16.1 gallons of real water and weighs roughly 185 lb once set up. It is a great size for schooling fish, corydoras groups and aquascapes — the most versatile small tank.
20 Gallon Long tank dimensions
| Inches | Centimeters | |
|---|---|---|
| Length | 30 in | 76.2 cm |
| Width (front to back) | 12 in | 30.5 cm |
| Height | 12 in | 30.5 cm |
| Footprint | 360 in² (2.5 ft²) | 2,323 cm² |
| Typical glass | 3/16 in | 5 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 | 18.7 | 70.8 |
| Filled 1 in below the rim | 16.1 | 61.0 |
| With 2 in of gravel | 13.1 | 49.7 |
Dose medication and fertilizer for the real water — about 13 gallons once the tank is aquascaped, not 19.
How much does a 20 gallon long tank weigh?
| Empty (estimated, 3/16 in glass) | 25 lb | 12 kg |
|---|---|---|
| Filled with fresh water | 160 lb | 73 kg |
| Set up, fresh water + 2 in gravel | 184 lb | 83 kg |
| Set up as saltwater | 186 lb | 85 kg |
| Floor load under the stand | 73 lb/ft² | 3.5 kPa |
Add rock, decor and the stand (often 40–120 lb). A floor load of 73 lb/ft² is 1.8× 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) | 25 W |
| 68 °F (10 °F lift) | 50 W |
| 63 °F (15 °F lift) | 75 W |
Colder room, nano heater or dual-heater setup? See the 20 gallon heater size chart.
Plan maintenance with the water change schedule: a 30% change on this tank is about 3.9 gallons.
Filter flow
| Tank type | Real flow | Filter rating |
|---|---|---|
| Community tropical | 64–97 GPH | 92–138 GPH |
| Planted tank | 81–129 GPH | 115–184 GPH |
| Goldfish, cichlids or heavy feeders | 129–161 GPH | 184–230 GPH |
Substrate
| Depth | Gravel | Sand |
|---|---|---|
| 1 in (2.5 cm) | 20 lb | 19 lb |
| 2 in (5.1 cm) | 40 lb | 39 lb |
| 3 in (7.6 cm) | 60 lb | 58 lb |
Stocking ideas
- 10 neon tetras + 6 bronze corydoras
- 8 zebra danios + 6 pygmy corydoras + 1 honey gourami
- 5 male guppies + 6 pygmy corydoras + 3 amano shrimp
Check any combination — including temperature and group size — in the stocking calculator.
Setup tips
- Its 30 × 12 inch footprint is the same as a 29-gallon, so one stand fits both and upgrading is easy.
- At 12 inches tall it is easy to light and reach — ideal for a first planted tank.
- Also popular for breeding, quarantine and small reptile set-ups because of the low height.
FAQ
What are the dimensions of a 20 gallon long fish tank?
A standard 20 gallon long glass tank measures 30 × 12 × 12 inches (76.2 × 30.5 × 30.5 cm) on the outside, a footprint of 2.5 square feet. Brands differ by up to about half an inch.
How much does a 20 gallon long fish tank weigh?
About 25 lb empty, 160 lb filled with water and roughly 185 lb set up with 2 inches of gravel, before rock, decor and the stand.
How many gallons does a 20 gallon long tank really hold?
18.7 gallons by its outside dimensions, about 16.1 gallons (61 liters) filled an inch below the rim, and about 13.1 gallons with 2 inches of gravel.
What size heater does a 20 gallon long tank need?
50 W to hold 78 °F in a 68 °F room; 25 W in a 73 °F room and 75 W in a 63 °F room.
How much gravel or sand for a 20 gallon long tank?
About 20 lb of gravel per inch of depth: 40 lb for a 2-inch bed, or 39 lb of sand.
What filter flow does a 20 gallon long tank need?
64–97 GPH of real flow for a community tank (4–6× turnover), so choose a filter rated about 92–138 GPH.