The 20 gallon long and the 29 gallon are two of the most popular tanks for a first community aquarium. They share the same footprint, so the choice comes down to height, volume and what you want to keep.
Side-by-side comparison
| 20 gallon long | 29 gallon | |
|---|---|---|
| Dimensions (L x W x H) | 30 x 12 x 12 in | 30 x 12 x 18 in |
| Footprint | 360 sq in | 360 sq in |
| Water weight | 167 lb | 242 lb |
| Full weight with 2 in gravel | about 233 lb | about 324 lb |
| Gravel for 2 in bed | about 42 lb | about 42 lb |
| Heater (3–5 W per gallon) | 100 W | 150 W |
| Filter flow (4–6x per hour) | 80–120 GPH | 116–174 GPH |
Typical standard sizes. Check your tank's label; brands vary slightly.
Why the 20 long is popular
- Low height makes it easy to reach the bottom for planting and cleaning.
- Light reaches the substrate easily, which helps carpeting plants.
- It suits bottom dwellers and shallow-water fish such as corydoras, kuhli loaches and shrimp.
- It's lighter, so more furniture-grade stands and shelves can take it.
Why choose the 29 gallon
- About 9 more gallons of water keeps temperature and water quality more stable.
- Extra height gives mid-water and taller fish more room.
- It fits the same footprint, so it's an easy upgrade later.
Which should you buy?
Choose the 20 long for a planted tank, shrimp, or bottom-dwelling fish, or if you want easy maintenance. Choose the 29 gallon if you want a mixed community tank with more swimming height and a little more margin for error. Either way, use the substrate calculator to plan your gravel and check the stand's weight rating.
Weighing up other sizes? See the tank size chart or the fish tank weight guide.
Frequently asked questions
Is a 29 gallon the same size as a 20 long?
They have the same 30 x 12 inch footprint, but the 29 gallon is 18 inches tall and the 20 long is 12 inches tall. The 29 holds about 9 gallons more.
Can a 29 gallon go on a 20 long stand?
The footprint matches, but a full 29 gallon weighs about 90 lb more. Only use the stand if it is rated for the 29 gallon's full weight.
Which is better for shrimp or bottom dwellers?
Both have the same floor area, so bottom dwellers get the same space. The 20 long is easier to reach into and light for plants; the 29 holds more water for stability.