How big do goldfish get? Some can be massive!

People often think that goldfish only ever grow to be a few inches long. Sadly, this is because most pet goldfish don’t live long enough to grow beyond this. However, with good care, goldfish have the potential to be much larger.

Common goldfish can easily grow to be 10 inches long and fancy varieties can reach 8 inches.

And these aren’t maximum limits! They’re fairly standard sizes, with some fish growing to be even larger…

How big was the biggest goldfish ever?

The wild goldfish pictured below was reported to be 14 inches long.

14 inch long wild goldfish
This wild goldfish measured around 14 inches (Photo courtesy of Buffalo Niagara Waterkeeper)

A pet goldfish in the UK was reported to be 15 inches long.

And the biggest goldfish ever recorded – the official world record – was a gigantic 18.7 inches!

These potential sizes are why we encourage all of our readers to buy a good sized tank or to keep their fish in a pond. It’s vital to ensure they have plenty of room.

While it is true that fish will become stunted if kept in smaller tanks, we consider this practice to be cruel and bad for your fish. You should always give your pets the space they need. This allows them to grow to their full potential.

Why do they get so big?

Genetics is a factor. Some individuals simply have the potential to grow bigger than others depending on their genes.

However, all healthy goldies could grow to several inches long if they receive the right care.

Goldfish will naturally grow to a large size when they are well looked after and given the right conditions to live in. These conditions include plenty of pond or tank space, good water quality, warm water temperatures, and a supply of nutritious food.

Goldfish Growth Rate

The average growth rate of a goldfish is about one inch per year.

Baby goldfish grow very rapidly in their first few months. Then their growth rate slows as they get older.

There are ways to make your goldfish grow faster but remember: you should always aim to provide your fish with the best possible care.

You shouldn’t try to stunt their growth to keep them small or overfeed them to make them grow. You will only end up harming them.

That said, if you really want a big goldfish – and you want to make them grow faster – there are some things you can do to safely influence your goldfish’s growth rate.

Next, we’re going to explore the five factors that influence growth rate.

How do you make goldfish grow faster?

The key to making goldfish grow faster is a good diet combined with lots of tank space, warm water temperature, and good water quality.

It also helps to choose fish with the right genetics. However, you will need to go to a specialist breeder to have any chance of knowing whether your particular pet had large parents!

Let’s look at the five factors that influence goldfish growth rate in more detail.

#1: Nutrition

Having a good diet is very important.  Serious breeders feed goldfish fry a high protein diet of live foods, such as micro-worms and baby brine shrimp. This stimulates growth and helps to produce the largest fish.

The runts in a spawn, who do not get as much food as the others, will not reach the size of their siblings. Because of a poor diet when they were young, some fry will never reach more than a few inches long for the rest of their lives.

A nutritious diet plays a big part in the growth rate throughout your fish’s life. This is why feeding good food is a must.  Live foods and veggies, in addition to a good protein staples, like pellets, can help your fish grow.

However, you must be careful to never overfeed them! Overfeeding will pollute your water and cause your fish to become constipated.

#2: Tank Size

Many goldfish have the potential to reach an impressive size, but then their owners buy an undersized tank or add too many fish.

Not having enough tank space will stunt your fish’s growth. Their activity will be restricted, meaning they get less exercise, and growth-inhibiting hormones will build up in a tank that is packed with too many fish.

Sadly, stunted goldfish are permanently impacted and the damage is irreversible. You therefore need to give your fish plenty of space from a very young age and throughout its life.

#3: Temperature

Temperature plays a big role in growth rate.

Goldfish kept in warmer water temperatures consume more oxygen, eat more food, and are generally more active. All of this helps them to grow to a large size.

Water temperature in the mid-70s Fahrenheit (mid-20s Celsius) is ideal.

#4: Genetics

As we mentioned earlier, the growth potential of your fish is limited by their genetics.

Unfortunately, unless you are a goldfish breeder, you really can’t do much about this one!

All you can do is buy your goldfish from a quality breeder, rather than a chain store. This will give you a better chance of finding a fish with good genes and which hasn’t already been stunted by poor conditions.

#5: Water Quality

Maintaining good water quality is not only vital to your fish’s health, it plays a role in their growth too.

When toxins are present in the water, goldfish cannot grow normally and must channel their strength to survive. You can get rid of these toxins by cycling your tank and doing weekly water changes. This will improve your water quality and allow your fish to put more of its energy into growing big and strong.

How to Measure a Goldfish

Accurately measuring a goldfish is crucial for tracking its growth. Fish keepers can employ various techniques and tools to obtain precise measurements. Understanding the proper methods for measuring ensures reliable data for assessing a goldfish’s size.


In conclusion, the size of goldfish is a multifaceted aspect influenced by genetics, environment, and care practices. Providing optimal conditions, from an appropriately sized aquarium to a nutritious diet, is essential for ensuring the well-being and growth of these captivating aquatic pets. By dispelling common myths and understanding the factors that contribute to goldfish size, fish keepers can create a thriving environment for their goldfish companions.


  1. How big is a full-grown goldfish?
    • A full-grown goldfish can vary in size depending on the breed, but on average, they range from 6 to 8 inches. Some larger breeds can reach lengths of 12 inches or more.
  2. How long does it take for goldfish to reach full size?
    • The time it takes for goldfish to reach full size varies based on factors like genetics, environment, and diet. On average, it can take anywhere from one to two years for goldfish to reach their full size, but some breeds may continue to grow throughout their lives.
  3. What is the maximum size of a goldfish?
    • The maximum size of a goldfish is influenced by factors such as genetics, living conditions, and care. Common goldfish varieties can reach lengths of 12 to 14 inches, while larger varieties like the Comet or Shubunkin can exceed 18 inches under optimal conditions.
  4. Do goldfish grow bigger in ponds?
    • Yes, goldfish have the potential to grow larger in ponds compared to confined spaces like tanks. Ponds provide a more natural environment with ample space, which allows goldfish to exhibit their full growth potential. However, it’s important to note that the rate of growth can still be influenced by factors such as genetics and nutrition.

How big is your fish?

Add a comment to let us and other readers know how big your largest goldfish is.

18 thoughts on “How big do goldfish get? Some can be massive!”

  1. My goldfish is 4.5 inches in a 55-gallon tank. He gets feed 3 times a day, enjoys the flakes. He also eats meal worms every wensday for protein. He has one tank buddy, a betta 2 inches. I was surprised they didn’t fight.

    • Betta and goldfish sadly do not make good tank mates. Unfortunately, bettas prefer warmer waters 76-82 whereas goldfish top off around 74. Even with this slight temperature difference, goldfish grow to be much larger than bettas. Not to mention, all goldfish are opportunists. A quick google search will tell you that these fish shouldn’t ideally be kept together!

      • Hi Gilby,

        we have actually had some luck with keeping bettas and goldfish together at times, but are aware that it is not ideal.
        To do it we kept the tanks at around 24C and had it heavily planted with a sponge filter, the goldfish we had were baby fantails and they didn’t bother the betta much at all, so they can be okay for a time given circumstances.

        Going forward however, you are absolutely right, we would definitely not keep adult goldfish with a betta and would never recommend keeping goldfish and bettas together to people, unless they are well experienced and know what they are doing, it usually isn’t a good idea.

  2. My gold fish are 1 1/2 yrs old. Live in an 700 gallon pond and are now roughly 6+ inches long, 2+ inches deep. Switched them to pellets a few months ago (another growth spurt). Loving them! So fun, so active and come to me when I call them.

  3. I have 10 goldies in about 400 gallon pond… doing great after buying as feeder money more than 1 1/2 inches long… they are 4-6 inches now after 1 year and have just spawned with 5 survivors. I would guess my biggest is closer to 7” as it is hard to tell in the water

  4. Our goldfish is around 10 inches long in a 660 gallon pond. He’s a common goldfish we dubbed ‘Bruce’. He’s around 5 years old, so we’re curious how much bigger he’ll grow?

    • Hi Emma, thanks for your comment,
      Goldfish can vary in size depending on the individual, some specimens can reach huge sizes, some exceeding 15″ while some stay smaller. As long as they continue to receive good care, clean water and decent food, they may still continue to grow, it is really down to the individual.

  5. Our family’s goldfish died last year around the age of 25 and about 12” long. We think she was won by my brother at a school carnival when she was a tiny feeder fish, but can’t remember what year for sure.

    She lived with a few other goldfish to begin with, and then was the last one standing in the same 40 gal tank for nearly two decades.

    • wow, that’s amazing to hear, we don’t normally see goldfish live for so long and get so large in a tank this size, well done!

  6. I hand 7 gold fish that I got at Petco they all started less then 1 inch now it’s down to 5 and the 2 biggest ones are 7 Inch long the others are 1 inch smaller then the bigger one they live in a 55 gallon tank

  7. My Steven was won at a carnival in 2018. Approximately 1.5 inches when brought home . He is now just over 10 inches long and 4.5 inches from belly to top. He is currently in a 38 gallon aquarium. Will be stepping up to a 55 gallon soon to keep him comfortable and healthy. I noticed after buying a good filtration system that his growth rate increased rapidly . With this being his fourth tank I can tell when it’s time to upsize as the PH levels get harder to maintain due to the waist he produces .He is definitely part of the family now and hopefully will be for many more years to come

  8. my goldfish are 8 centimeters i have 2 a male and a female they live in a 60 litre tank they are both one year old

  9. My common goldfish Hoover is 9 years old, close to 9” long in a 15 gallon tank. I siphon waste and old food everyday and water parameters are perfect! He shares his tank with 2 nerite snails, is wonderfully interactive (we watch Netflix on my iPad!) super fun and I love him dearly!!!

  10. I forgot to say that I feed Hoover 2-3 frozen peas and Mizuho pellets for breakfast and a rotation of frozen bloodworms, mysis shrimp and brine shrimp for dinner and more pellets for a midnight snack as we watch movies on Netflix!. I love him so!!!

  11. My goldfish is 5 1/2 inches! He was 1 inch when I bought him, he is currently in a 20 gallon tall, and next week he’ll be in a 75 gallon and eats Flakes, Pellets, shrimp/blood worms, and Broccoli about once a week

  12. My goldfish are 1 inch long and get normal fish food and I’m surprised that they are nudging each other and there are 2 goldfish in the tank


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