How Big Do Goldfish Get? Potential Size and Growth Rate (2024)

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Featured Image – PT-0109 – how big do goldfish get
Dr. Mollie Newton
Published by Dr. Mollie Newton PHD| Senior Editor
Last updated: May 7, 2024
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Goldfish are usually cherished by everyone, right? They’re charming, require little upkeep, and are simple to please, thereby making them an excellent introductory fish for those commencing an enduring aquarium hobby. Despite their uncomplicated disposition, they offer their own distinct challenges and frequently arouse interest. A common query that we often come across is “how big can goldfish get?”

Article Summary

  • Goldfish can vary in size depending on factors like genetics, tank size, nutrition, water temperature, and water quality.
  • Most common pet goldfish will reach a size of around 6-10 inches in captivity.
  • The largest recorded goldfish reached a length of 18.7 inches, though this is not typical for aquarium goldfish.

Follow along through today’s article as we take a deep dive into just how large goldfish get.

How Big Does a Common Goldfish Get?

Goldfish Swimming in a Tank

Originally bred from wild carp, the pet goldfish we know and love today have progressed through time from their wild ancestors, through beautifully bred koi carp (aka common carp) of China and East Asia.

These wild goldfish were selected for their appearance and capacity to grow quite large, which lends to some very large possibilities in today’s modern goldfish.

Due to their limited genetics and stunted growth capability from captive breeding, most comet goldfish will only reach around 6-8 inches in length.

Comet Goldfish

The comet tailed goldfish, a common variety sold in most pet stores, is what people tend to think of when they think of “goldfish.”

These start as small goldfish around 2” in length and most people assume they’ll stay that way, but these fish can surprise their owners when they reach sizes of over 10 inches!


Other breeds of goldfish can be smaller or larger than this average, and it’s important to do your homework beforehand when looking at exactly what fish you’d like to have in your home.

Talking to your local pet store is a great start, as they’ll have hands-on experience in handling the particular fish that they may be selling.

Average Weight Of A Goldfish

On average and given adequate food, most goldfish will weigh somewhere around eight ounces, with giant goldfish having the potential to weigh much more (up to 3-4 pounds total in some cases.) 

Creating a healthy environment is one of the keys to maximizing the weight of your home goldfish.

This weight is dependent on the growth of your goldfish and can vary depending on the amount of food, living conditions, and general health of your fish over time. 

How Big Goldfish Get In a Tank

While the common myth about your typical feeder goldfish growing to massive sizes only based on a larger tank size is mostly untrue, there is some kernel of honesty to it.

In general, fish kept in a small tank or fish that live in a fish bowl will tend to stay small (think 2-6”).

A bigger tank means more room for them to move, as well. Goldfish kept in a large tank with fresh, clean tank water have the capacity to grow larger than those in smaller tanks.

How Big Goldfish Get In The Wild

Oranda Goldfish
Oranda Goldfish

Goldfish living in outdoor ponds or natural environments have the ability to make it to much larger sizes, up to the 15-16” mark.

This is primarily due to the increase in water quality found outdoors.

Cold water brought in from rain and natural sources has increased amounts of oxygen, meaning that the goldfish is able to function more in a more capable manner than in the home aquarium. 

Additionally, the natural goldfish diet options for protein sources are generally more diverse in the local pond than at home, and this new varied diet can lead to a real explosion of growth.

Is it okay to release goldfish to the wild?

An important thing to note is that we should never release our goldfish into wild ponds and lakes because of this growth capacity!

Without larger predatory fish to keep them in check, goldfish can grow and reproduce rapidly, quickly throwing off the delicate balance of these once-pristine natural waterways.

Your local lake is not a good place to dispose of your fancy goldfish if you can no longer hold them properly in a home goldfish tank! Consider looking online or at a local pet store for a place to rehome your pet fish if you can’t take care of them any more.

Home Aquarium

While your home fish aquarium setup may have a great filtration system and be able to handle quite a bit of waste, it’s hard to compete with the natural capacity that flowing water and rain have for providing an oxygen and food rich environment for goldfish.

This is why when designing a home system, we seek to do our best to emulate a natural one by providing artificial water movement with bubblers and pumps, along with the most nutritious food possible.

How Big is the Biggest Goldfish Ever Recorded?

The largest goldfish ever recorded reached a length of 18.7 inches in length! While this isn’t necessarily something that every aquarium goldfish owner should plan for, it’s important to keep in mind when thinking about just how big these fish can get.

To help you visualize how big goldfish can get, check out this cool video…

Goldfish World Championship CIPS 2019 – Aquarium Co-Op​

How Long Does It Take For a Goldfish to Reach Full Size?

Most goldfish grow fairly quickly upon hatching, up to 1-4” in their first few months of life in the tank.

From there, this growth rate will usually slow and they’ll add an additional 1 inch in length each year after that. Some fancy goldfish may see a variation in this rate, depending on breed.

Unlike some other species which can tend to grow in spurts, goldfish will usually maintain an average speed of growth over time.


This can vary somewhat through the seasons with temperatures,especially for those kept in outdoor ponds, with average goldfish growth increasing in the warmer months and slowing as they reach a torpor state in the winter.

Likewise, periods of greater access to food, higher amounts of oxygen, and cleaner water will allow goldfish to grow faster than they would otherwise.

How Do I Make My Goldfish Grow to Full Size?

Along with generally keeping a good eye on your pet goldfish, there are several other factors to consider when looking at the question of how big do goldfish get.

The main things to look at when trying to get healthy, large goldfish are genetics, space in your tank, nutrition, the water temperature, and water quality inside of your tank.


Breed and genetics have a huge role to play in the growth of your fish. Inbred feeder goldfish from the average pet store will typically never reach the same size as those which have been carefully bred, having been selected more for fast reproduction than size.

Properly bred comet goldfish from a reliable source will be able to grow much more ably than their inbred counterparts.

Tank Size

A minimum of a 30 gallon tank is a good place to start for a single goldfish looking to reach its maximum size, with 10 gallons of additional water per goldfish or tank mate after that.

Going smaller than this means your fancy goldfish may not have enough room for their own sense of space, and other goldfish will become crowded in their small bowl.

It is also recommended to take into account your fish’s behavior when making your aquarium, as this can offer valuable information in determining the appropriate tank size, particularly when introducing new aquarium neighbors.


Food for Aquarium fish
Food for Aquarium fish

Adequate nutrition with food is key for having a goldfish reach its largest size.

Feeding your goldfish a quality amount of varied food, including flakes, live foods, and pellets will ensure that its nutritional needs are met, allowing the fish to grow properly.

Also, make sure to be feeding your goldfish at the right interval as overfeeding will lead to a rapid increase in size as the fish bloats, but ultimately affect its health as it struggles to breathe and function.


As a cold water fish species in their natural environment, goldfish thrive best in temperatures between 50-60 degrees. While they can handle some variations in this temperature, any colder and their metabolism will naturally slow down, as will their growth. Be careful of adjusting temperature too much. Fish may become stressed and experience temperature shock, which can sometimes result in goldfish death due to excessive temperatures or abrupt temperature fluctuations.


If keeping fish in an outdoor pond, make sure that there is some form of temperature regulation such as a heating unit in order to maximize the growth rate of your fish.

Water Quality

One of the most important components of goldfish keeping, ensuring that the water in your tank is clean and fresh with the use of filter sponges and a good system is incredibly important.

Dirty water in your tank will not only slow the growth of your goldfish (and different species) but can lead to an increase in disease and infections.

Weekly water changes are a great way to start, along with continuous monitoring of factors such as pH, ammonia, and oxygen levels within your tank. Having live aquatic plants in your goldfish aquarium can also help improve your aquarium’s water quality.

Remember, pet goldfish grow best with clean water!


Today, we’ve looked at how big do goldfish get in detail. In general, most goldfish grow at a constant rate, and will reach a maximum size of around 6-10” in captivity, depending on how well they are fed, available space and genetics.

A big takeaway is to make sure that you know the species you’re buying, as a fancy goldfish with a good background of health will likely grow larger than a cheap, inbred one.

Feel Free To Share!

As always, we’d like to say thank you for reading along with today’s article on how big do goldfish get!

If you found this information useful, feel free to share it with other fish fanatics and join us next time as we continue our aquarium adventures.

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