A fully grown male Betta splendens can grow up to three inches in length.
However, most adult betta fish will be smaller than this, and various factors will influence how large your betta will get.
Let’s look a little closer to get size-wise on this little pet fish with a big personality!
The Average Size of a Mature Betta
Although bettas can reach three inches long, the average-sized fully grown male is only around 2.25 – 2.5 inches in length. Female betta fish are usually a little smaller still, often only reaching two inches at full maturity.
Why Are Some Bettas Bigger Than Others?
The eventual size of your betta is a combination of two factors: genetics and environment.
Humans have kept bettas for a long time. A thousand years of domestication and selective breeding have produced a vast array of betta variants. Just as a Chihuahua will be a different size from a Labrador, selective breeding in bettas has produced breeds of various sizes.
The environment a betta is raised in will also contribute greatly to its maximum growth rate and final adult size. A high protein diet, adequate space to swim, and good water quality will all play a key role in determining a betta’s size and long-term health as an adult.
If you buy your betta from a certified pet store, most of that will have already been determined by the level of care given to the fish by the breeders and suppliers.
How Big Will Your Betta Be When You Buy Him?
Bettas are typically sold when they’re between six and twelve months old, so they’ll often be fully grown when you receive them. Therefore, choosing a reputable supplier is key to purchasing a healthy fish that hasn’t been stunted by poor care.
If you’d like to nurture your bettas from a tender age, you can now order baby bettas from online pet stores such as Petco or, even better, breed your own!
How Fast Do Baby Betta Fish Grow?
Baby fish grow at a phenomenal rate! When betta fish hatch, they’re a tiny 0.1 inches long. Yet at six weeks, they can be ten times that size, with the largest specimens already exceeding an inch!
At 12 weeks, the fastest growers can have reached two inches, at which point the growth rate slows down. Of course, all of this depends on the quality of care and diet the baby bettas receive from the moment they hatch.
Pristine water conditions, correct water temperature, and protein-rich foods such as vinegar eels, brine shrimp, and micro worms will do wonders to help baby bettas grow to their greatest potential size, strength, and glorious colors.
When Is a Betta Fish Fully Grown?
A betta is considered fully grown at thirty weeks or seven months, although there are exceptional cases of individuals that keep growing until around the fourteen-month mark.
To put this timeline into perspective, domestic bettas typically live for 2-5 years. Even if a few individuals make it to their 10th birthday, it’s still a short lifespan, and you can see why they need to grow up so fast!
Why Is My Betta Getting Fatter?
After 14 months, you can be sure your betta won’t grow any longer, although they may continue growing in weight through overfeeding or a poor-quality diet!
Proper feeding is one of the most critical factors in keeping your betta fish healthy, happy, and in good shape. Read our complete guide on what and how much to feed a betta fish.
Is a Bigger Betta Actually Better?
One of the reasons that enthusiasts like to compare the size of their bettas is the prestige attached to large males. In their native lands, betta fish are wagered upon in fighting contests – earning them their other popular name, ‘Siamese fighting fish,’ so it’s fair to say there’s a bit of bravado about having the biggest and best betta around!
Scientific studies have shown that larger males are more aggressive than their smaller counterparts. Yet it’s wise to remember that a dominating character might not be the ideal attribute for a community tank situation.
If you have other community fish species living in the same fish tank alongside your betta, you might be better off choosing a small to medium-sized betta fish such as Betta imbelis, also known as the ‘Peaceful betta.’
On the other hand, If you just want a few robust snails as tankmates for a big, feisty betta, then, by all means, go big!
What Is the Maximum Tank Size for a Betta Fish?
There’s no real limit to how big your betta tank should be. It comes down to your budget, personal preference, and how much maintenance you’re willing to do.
However, an overly large tank may make your betta appear smaller and more distant amidst the vast body of water.
Five gallons is often quoted as the smallest possible size to house a single betta fish, but a 10-gallon tank will give him additional space to explore, along with aquatic plants and rocks for hiding places. A 20 or 30-gallon tank also adds the option of introducing a few choice tankmates.
Check out our recommendations for great betta tanks here!
A Note on Giant Betta Fish
If you’re looking at our pages, we’re guessing you’re most interested in the famous Betta splendens, aka ‘Siamese fighting fish’ or even ‘Japanese fighting fish.’ However, another species of betta can grow much bigger than a Betta splendens; the Betta anabantoids, aka ‘Giant betta.’
Modern breeding work has helped these titans to grow to a whopping seven inches! They are, however, rather a different fish in temperament and appearance to your everyday betta and require a much larger tank.
Bigger Isn’t Always Betta!
Whatever their size, these popular aquarium fish are big characters that come in small packages!
While you may enjoy showing off your monster 3-inch specimen, there’s also nothing wrong with having a petite betta. In fact, in a community environment, it may even be better!