A 5 gallon aquarium is small enough to fit on a desk or shelf, but large enough for a single fish or a few small ones
A 5 gallon aquarium holds 5 US gallons of water, which equals about 19 liters or 640 fluid ounces. In physical dimensions, a standard rectangular 5 gallon tank measures roughly 16 inches long, 8 inches wide, and 10 inches tall—though exact measurements vary by manufacturer and tank shape. If you have seen a milk jug, a 5 gallon aquarium holds the same volume as one of those jugs filled with water.
The footprint (the space it takes up on a surface) is what matters most when you are deciding where to put it. A 5 gallon tank occupies about 128 square inches of table or shelf space—smaller than a standard sheet of paper laid flat. The weight when full is roughly 40 pounds, so you need a sturdy surface that can handle that load without sagging.
Key Takeaways
- A 5 gallon aquarium measures approximately 16 by 8 by 10 inches and weighs about 40 pounds when filled with water.
- The tank is suitable for one betta fish, one small goldfish, or a small group of nano fish like tetras or rasboras, but not for larger or more numerous fish.
- Water quality in a small tank changes quickly, so you will need a filter and regular water changes to keep fish healthy.
- A 5 gallon tank costs between $30 and $80 for a basic setup, depending on whether it includes a filter and heater.
What fish can actually live in 5 gallons
A single betta fish is the most common choice for a 5 gallon tank. Bettas are colorful, hardy, and do not need a heater or filter to survive—though both make the tank easier to maintain. A betta will live 3 to 5 years in a 5 gallon tank with regular water changes.
Small groups of nano fish also work in 5 gallons. Neon tetras, cardinal tetras, and rasboras are schooling fish that do better in groups of 6 to 10, and they stay small enough that a 5 gallon tank can house them if you do not overstock. Corydoras catfish are bottom-feeders that can live alongside tetras and help keep the tank clean by eating uneaten food.
A single small goldfish can live in 5 gallons temporarily, but goldfish grow quickly and produce a lot of waste. Most experts recommend at least 20 gallons for a goldfish long-term. If you start with a goldfish in a 5 gallon tank, plan to move it to a larger tank within a year.
Fish to avoid in 5 gallons include cichlids, plecos, and any fish longer than 2 inches that are not part of a schooling group. These fish either grow too large, are too aggressive, or produce too much waste for the small volume.
Why water quality matters more in a small tank
A 5 gallon tank has less water to absorb fish waste, uneaten food, and other pollutants. In a larger tank, these waste products get diluted across more water, so they build up slowly. In a 5 gallon tank, they build up fast, and the water can become toxic within days if you do not remove it.
This is why a filter is important even though some fish (like bettas) can technically survive without one. A filter removes solid waste and helps beneficial bacteria break down ammonia and nitrite—the toxic compounds that kill fish. Without a filter, you need to do a 50 percent water change at least twice a week to keep the tank safe.
With a filter, you can usually get away with one 25 percent water change per week. A filter also keeps the water moving, which helps oxygen dissolve into it—something fish need to breathe. Even a small hang-on-back filter or sponge filter designed for 5 to 10 gallon tanks will make a real difference in how stable the tank stays.
Tank shape and how it affects usable space
Not all 5 gallon tanks are the same shape. A standard rectangular tank is 16 by 8 by 10 inches. A cube-shaped 5 gallon tank might be 10 by 10 by 10 inches. A tall, narrow 5 gallon tank might be 12 by 6 by 14 inches. The volume is the same, but the shape changes how much room your fish actually has to swim.
Fish prefer tanks that are longer rather than taller. A long, shallow tank gives fish more horizontal swimming space, which they use more than vertical space. A tall, narrow tank looks impressive but gives fish less room to move around. If you are choosing between two 5 gallon tanks, pick the one with the longer footprint.
Cube tanks and bowls are popular because they look nice on a desk, but they are harder to maintain. The smaller surface area means less gas exchange (oxygen in, carbon dioxide out), so the water can become stagnant faster. If you choose a cube or bowl, a filter becomes even more important.
Cost and what comes in a basic setup
A bare 5 gallon tank (just the glass or acrylic) costs $20 to $40. A basic kit that includes the tank, a small filter, a heater, and a light costs $50 to $100. A premium kit with better equipment costs $100 to $150 or more.
Beyond the tank itself, you will need substrate (gravel or sand for the bottom), which costs $5 to $15. A heater is optional if you keep the tank in a warm room, but it costs $15 to $30 if you want one. Decorations, plants, and hiding spots cost $10 to $50 depending on what you choose. The ongoing cost is mainly food ($5 to $10 per month) and replacement filter media ($5 to $10 every month or two). Water conditioner to remove chlorine from tap water costs $10 to $20 per bottle and lasts several months. A basic 5 gallon setup is one of the cheapest ways to keep fish, which is why it is popular for beginners.
How a 5 gallon tank compares to other sizes
A 10 gallon tank is only twice the volume but gives you much more flexibility in what fish you can keep. A 20 gallon tank is the minimum for most community setups where you want multiple species living together. The table below shows how tank size affects what you can keep and what equipment you need.
| Tank Size | Dimensions (approximate) | Best For | Filter Needed |
|---|---|---|---|
| 5 gallons | 16 × 8 × 10 inches | One betta or small group of nano fish | Recommended but optional |
| 10 gallons | 20 × 10 × 12 inches | One goldfish or larger group of small fish | Recommended |
| 20 gallons | 24 × 12 × 16 inches | Multiple goldfish or a diverse community | Required |
| 40 gallons | 36 × 18 × 18 inches | Larger fish or many smaller fish | Required |
If you are just starting out and unsure what you want, a 5 gallon tank is a good way to learn the basics of fish care. However, plan to upgrade if you want more fish or larger species down the road.
Frequently Asked Questions
Can I keep two betta fish in a 5 gallon tank?
No. Male bettas are extremely territorial and will fight to the death if confined together. Female bettas can sometimes live in groups called "sororities," but this requires careful setup, constant monitoring, and at least 20 gallons. A 5 gallon tank is too small and stressful for any betta pairing.
Do I need a heater for a 5 gallon tank?
It depends on the fish and your room temperature. Bettas, tetras, and rasboras prefer water between 75 and 80 degrees Fahrenheit. If your home stays in that range, you may not need a heater. If your room is cooler, a small heater keeps the water stable and the fish healthy.
How often should I change the water in a 5 gallon tank?
With a filter, do a 25 percent water change once a week. Without a filter, do a 50 percent water change twice a week. If you notice the water smells bad or looks cloudy, change it sooner. The smaller the tank, the more often you need to maintain it.
Can I use a 5 gallon tank for shrimp or snails instead of fish?
Yes. Freshwater shrimp and snails are good choices for small tanks because they produce less waste than fish and do not need as much space. A 5 gallon tank can hold 10 to 20 small shrimp or several snails. They are quieter than fish and interesting to watch, though they are less interactive.
What is the difference between a 5 gallon tank and a 5 gallon bowl?
A bowl has no corners and a smaller surface area, which means less oxygen exchange and harder water maintenance. Bowls also have no room for a filter. A rectangular tank is easier to maintain, holds a filter, and gives fish more usable swimming space. If you want a 5 gallon setup, a tank is better than a bowl.