Guppy Fish Size Chart – How Big do Guppies Get?

Guppies vary in size, but on average, males are 0.6–1.4 inches long, while females measure around 1.2–2.4 inches. Some strains of guppy fish are even selectively bread for their size. Guppies with a suitable genetic background can grow up to 2.5-3 inches, but that’s not something you’ll see every day.

Nobody can tell how large your guppies will be when reaching adulthood, but there are some steps you can take to ensure the best possible growth and development. If you’re worried that your guppies aren’t growing properly, or you just want to take all the precautions to avoid potential problems, then I’m here to help!

In this article, I’ll talk about the most probable factors that cause stunted growth in fish, as well as the best solutions and some additional tips for growing happy, healthy guppies. Keep reading to find out how to help your guppies reach their full growth potential!

Guppy Fish Size Chart by Age

Guppy Age Guppy Size
Newborn guppy 1/4 inches (6 mm)
1 month old guppy 1/4 and 2/3 inches (0.6- 1.5 cm)
2 months old guppy 1/2 and 3/4 inches (1.2 to 2 cm)
6 months old guppy 1.5-2 inches (4-6 cm)

At around 6 months old, guppies become adults and they stop growing. It is possible that guppies will still grow after 6 months, but generally, only their fins get longer, while their body size remains the same.

Why Guppies Don’t Grow Properly?

You must first pinpoint the source of the problem before doing anything else. That’s why I’ll first go through a list of the most probable causes for your guppies’ stunted growth. But this information isn’t only related to guppies! These factors also apply to the development of any other fish species.

You might be dealing with only one, or multiple of these problems simultaneously. Luckily, most of them are easy to fix. So, let’s see! What are some of the most common reasons why guppies don’t grow properly?

– Unsuitable Water Parameters

Water quality plays a huge role in the health and proper growth of your fish. All fish species have their unique water quality requirements, and guppies are no different. Any fluctuation in water temperature, hardness, pH, oxygen levels, or trace chemicals can shock your fish. For more in-depth information on guppy water parameters, check out my other articles on how to care for guppies.

Lack of oxygen, low temperatures, increased acidity, and toxin build-up are some of the biggest reasons for poor health and growth in guppies. That’s why your aquarium should be fully equipped from day 1. Things like a water filter, a heater, and an air pump are indispensable, especially for big aquariums. Completing at least a weekly water change and keeping the aquariums clean is also crucial to maintain good water quality.

– Poor Diet

This goes without saying, but all animals need a wide variety of vitamins, minerals, and macronutrients to sustain proper growth. A monotonous diet, especially based on low-quality flake food, is a recipe for disaster. Your guppies need a wide variety of nutrient-dense foods, including nutritious flakes, but also algae pellets, other frozen foods, and even live food.

You must also pay attention to the feeding frequency. Guppies are sturdy fish, and they can survive for long periods with little food. But during their growing stages, feeding is important. Growing guppies need plenty of food to thrive and fuel their growth. Make sure you provide your guppies a varied diet based on nutrient-dense foods. Feed them often, but not too much.

– Lack of Space

Guppies are tiny when compared to other fish, but they need plenty of space to move around and feed. A small aquarium or lack of space can impair your guppies’ growth in various ways, either by making feeding more difficult or by leading to fluctuations in water parameters.

It’s best if you allow 1-3 gallons of water for each guppy fry. That means that if you have a 10-gallon tank, you should only keep 3-5 guppies at most. And that’s if you have a good water filter. Guppy fry can survive with lower water volumes, but as they grow, feeding and aquarium maintenance will become more difficult.  If you plan to keep many fry, you’ll eventually have to upgrade to a larger aquarium

– Crowded Aquarium

This point on the list goes hand in hand with the lack of space. But I’d also have to add that lack of space isn’t only a problem for small aquariums. You can also encounter this problem if your aquarium is overly crowded.

The same issues apply to a large but crowded aquarium as well— poor water quality, difficulty feeding. Additional problems with crowded aquariums include low oxygen levels, stress, and ammonia build-up. The more fish sharing the same tank, the higher the competition for food, which can greatly stress your guppies.

Waste also becomes a problem. Although your filter might be appropriate for your tank size, if you have too many fish swimming around, you might still have too much ammonia in the water at times. Not only does dirty, ammonia-laced water lead to stunted growth. These fluctuations in water quality might even kill your fish down the line.

– Genetic Factors

Sometimes, guppies are just meant to be small. If your guppies aren’t genetically wired to grow larger than average, there’s not much you can do to turn things around. It could be that the specific guppies you have were selectively bred for their small size.

You could start breeding your guppies for larger sizes if you have enough patience and time on your hands. But that means you’ll need to go through multiple generations of selective breeding before you can enjoy big-sized guppy fish. Ensuring proper food and nutrient intake for gestating female guppies might also lead to better growth outcomes in fry.

How to Encourage Guppies’ Growth?

Now that we’ve got the “what not to do” part down, let’s see how to solve these problems. With a little bit of patience and troubleshooting, you should be able to get your guppies back on track! All you have to do is keep the following tips in mind.

– Monitor Water Parameters

Water quality is important, and any fluctuations in temperature, pH, hardness, oxygen, and toxin levels are to be avoided. You need to maintain the water parameters stable and within the optimal range for guppy health and development. To do that, you’ll need some extra aquarium equipment.

Water hardness and pH are probably the least problematic. In most areas, tap water is well within the proper range for guppy fish. However, you’ll need to install a heater to maintain a stable temperature. Guppies tend to live longer in slightly colder water, but for proper development, warmer water is better.

An air pump will help you maintain stable oxygen levels in the tank, while a filter will keep the water clean a lot longer and prevent toxin buildup and pH drops. For extra help filtering the water, you can also add some non-toxic live plants. You might also need to add a light source for the plants.

Perform weekly water changes of at least 20% volume. This will also remove toxins and dilute the water. Keep an eye on dirt buildup on tank walls, corners, the substrate, and any decorations in the water. Certain types of bacteria can create harmful by-products that increase water acidity. You’ll have to keep these surfaces clean.

– Improve Diet Quality

A poor diet can lead to deficiencies, stunted growth, and even growth defects in guppies. Offering your fish a wide variety of fresh, dried, and frozen food is non-negotiable if you want healthy, sturdy fish. You need to ensure that your fry get all the required micronutrients, protein, fat, and energy needed for proper bone and body development. Consider introducing some of the following superfoods in your guppies’ diet.

Brine shrimp is a great source of protein and fatty acids. Other great food sources for growing guppies include micro-worms, daphnia, egg yolks, and beef heart. These foods include all the water-soluble vitamins necessary for proper bone development, including vitamins A, D, E, and K.  However, as guppies are reaching maturity, you need to switch them to a lower-fat diet. These foods won’t lead to any growth spurts once your guppies are past their premature stage.

Another difference between growing and adult guppies is feeding frequency. While adults only need feeding once or twice a day, guppy fry should eat more frequently. I usually recommend feeding growing fry 5 times a day, based on my personal experience. I find that rotating between different types of nutrient-rich feed, 5 times a day, results in healthy, colorful guppies that grow to their full potential.

– Provide Enough Space

Your guppies need space to move around for healthy bone and muscle growth. Providing enough room is as easy as moving your guppies to a bigger tank, or separating your fish into multiple smaller tanks. If you’re unsure about the appropriate tank dimensions, a good figure to shoot for is 1-3 gallons of water for each guppy.

Remember that more is better than too little space, but also keep tank dimensions reasonable. You shouldn’t place your guppies in a tank that’s too large either. Large water volume also makes feeding more difficult for growing fish. Just stick to a happy medium.

– Separate Males and Females

Guppies are breeding machines. They reach sexual maturity at just 3 months of age, and male guppies are indiscriminate about their perfect mate, to say the least. Female guppies give birth to dozens of guppies at a time, and their gestation period lasts only about a month. If you keep male and female guppies in the same tank, you’ll soon have more fish than you or your aquarium can handle.

Breeding is a taxing process, especially for female guppies. It consumes a lot of energy and resources that could otherwise be redirected towards growth. And that’s even without saying that breeding can also shorten a guppy’s lifespan. For the best growth and health outcomes, one of the easiest things you can do is to separate your male and female guppies before they start breeding.

When Do Guppies Stop Growing?

Guppies reach full development at roughly 6 months old. Beyond this point, you won’t be able to grow your guppies any further. However, you might have some luck with male guppies, as they may keep growing longer fins and tails even after reaching adulthood, albeit for just a short period.

If your guppies have stunted growth but haven’t yet reached adulthood, they might be able to catch up with a proper diet before the 6-month mark. To give your small guppies the best chances of growing, you can also separate your fish by size. This way, the smaller guppies will also get a fair chance at feeding properly.


Genetics play a big role in how large guppy fish grow. But that’s only half of the story. The environment is another huge factor that determines health and growth. With the proper diet, water quality, and a low-stress habitat, you can support the optimal development of your guppies.

Hopefully, this article has helped you get a better picture of the factors that influence healthy guppy growth. Each of these factors is important and plays an important role by itself, but combined, they cause an even greater effect.

avatar Noah
I’m Noah, chief editor at VIVO Pets and the proud owner of a playful, energetic husky (Max). I’ve been a volunteer at Rex Animal Rescue for over 2 years. I love learning and writing about different animals that can be kept as pets. read more...

Questions and Answers

huh, then the 3 female guppies I had that were about 4 inches long were anomalies’ It was amusing to watch the males try to woo them.

Leave a Comment

Your email address will not be published. Required fields are marked *