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Goldfish Growth: Size, Growth & Weight Chart

Gregory Iacono

By Gregory Iacono


It’s been about 2,000 years since the goldfish was domesticated in China. Today, this illustrious fish is still going strong. You’ll find goldfish everywhere in the United States, and they’ve become as universal as baseball and apple pie.

With over 200 types of goldfish, it might be difficult to determine how big they get, but typically they can grow up to 8.5 inches and 15-18 ounces in weight. The information below will greatly help with all the growth data you need to know about these fantastic and fancy fish. If you’re setting up an aquarium or pond and looking for answers on the glorious goldfish, read on!

Goldfish Breed Overview

Goldfish are incredibly robust and can adapt to an unusually wide range of habitats, temperatures, and oxygen levels. If released into the wild, they adapt quickly and can just as quickly overturn the natural order, becoming a threat to local ecosystems.

In ponds and aquariums, goldfish are revered because of several factors. For example, they get along well with other fish, don’t need other goldfish to be happy and healthy, and are smarter than most fish species. Goldfish are so beloved that, in Paris, you can donate yours to the  Aquarium de Paris.1 They will gladly take the fish off your hands and add them to their goldfish population.

Goldfish will remain relatively small in a small tank, and vice versa. However, some released into the wild have grown to enormous proportions, at least for goldfish. Plus, as mentioned earlier, there are over 200 goldfish types, and some will grow much larger than others.

Goldfish swim in an aquarium
Image Credit: Val Krasn, Shutterstock

Goldfish Size & Growth Chart

Below are some typical numbers for most types of goldfish. It’s important to remember that they can grow faster and larger, depending on several factors, including their species, tank or pond size, water quality, etc.

Age Weight Range Length Range
1 month 0.107 ounces 0.9–1 inch
6 months 0.4 ounces 1.5–2 inches
12 months 1 ounce 2.5–2.8 inches
18 months 3 ounces 3.2–3.5 inches
24 months 6 ounces 4 inches
3 years 7 ounces 5 inches
4 years 10 ounces 6 inches
8 years 15–18 ounces 8.5 inches

When Does a Goldfish Stop Growing?

Although it’s commonly believed that goldfish grow to the size of their tank and then stop, the fact is that they never stop growing. The most significant factor in their growth is, not surprisingly, water quality. The better the water, the more your goldfish will grow. Eventually, they will outgrow a tank and need to be moved to a larger one or a pond.

Goldfish never stop growing because, like most fish species, they’re indeterminate growers. That means they grow quickly when young and then, rather than stopping like humans and most mammals, continue to grow for the rest of their lives. Many fish, amphibians, and reptiles do the same, and clams too!


The 4 Factors Affecting the Size of Goldfish

Several factors affect the eventual size of any goldfish, including their species, location, and several others. They include the following:

1. Water Quality

Water quality is the factor that affects goldfish growth the most and is also the reason most goldfish kept in bowls die so quickly and so young. Cloudy, unfiltered, or filthy water will stunt a goldfish’s growth. The pH of the water is also critical. Although goldfish can adjust to many pH levels, they do best with a pH of 6.5 to 7.5.

2. Food and Diet

It might surprise you that goldfish are omnivorous, which means they eat a wide variety of foods, including plants, insects, and animals. A well-rounded diet (see more below) will significantly affect the size of your goldfish. The better the food, the bigger the goldfish.

goldfish eating in the tank
Image Credit: oatpost, Shutterstock

3. The Category or Strain of Goldfish

Goldfish come in two strains: slim-bodied and fancy. Fancy goldfish come from hundreds of years of selective breeding and grow faster than slim-bodied, which are more like their wild cousins.

4. Tank or Pond Size

As we’ve seen, goldfish keep growing their entire lives, but they still grow more or less based on the size of their environment. Goldfish will get larger and do it faster in a larger tank or pond than in a smaller tank.

Ideal Diet for Maintaining a Healthy Weight

Any fish food you give your goldfish should have at least 30% protein and 12% fat to get the nutrition they need to stay healthy and grow normally. Commercial fish food does an excellent job of keeping these numbers in line, including flakes, pellets, and wafers.

Giving your goldfish live food like brine shrimp, daphnia, and others is also a good idea. Not only are these foods nutritious, but catching and eating them is similar to what they do in the wild and, thus, healthier for your goldfish. It’s also critical that you place green, leafy plants in your aquarium or pond. Your goldfish will gladly nibble on these all day between feedings, including:

  • Crinum calamistratum (African onion plant)
  • Anubias
  • Java Fern
  • Bolbitis Fern
  • Marimo Moss balls
Carassius auratus Goldfish_gunungkawi_shutterstock
Image Credit: gunungkawi, Shutterstock

How to Measure Your Goldfish

What you need to keep in mind when measuring a goldfish is that the tail fin length can, and will, vary significantly. For that reason, most goldfish experts like to measure their goldfish from the nose to the end of the peduncle, where the body and the tail meet.

An excellent example is comparing a 4-inch goldfish with a 3-inch tail to a 3-inch goldfish with a 4-inch tail. With the 4-inch body, the former will be heavier (and thus “bigger”) because the tail fins weigh almost nothing.

Final Thoughts

How big do goldfish get? There have been reports of some growing as big as 5 pounds, which is massive for a goldfish! The average is much smaller than that, usually due to the tank or pond where they live. What’s truly fascinating is that, under the right conditions, a goldfish will keep growing until it gulps its last breath of air.

As long as the water in your goldfish’s tank or pond is clean and the food it gets is healthy, your goldfish will grow throughout its life. In other words, much of their growth depends on you, their owner, so be sure to treat your goldfish well. The better the conditions and food, the bigger and prettier your goldfish will grow!

Featured Image Credit: Hans Braxmeier, Pixabay

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