Guppy Size: How Big Do Guppies Get?

Guppy fish have a lifespan of 2-5 years depending on their genetics, diet, and living conditions. If you’re a beginner fishkeeper, you must be wondering how big your guppies will grow and after how long.

Female guppies are bigger than male guppies. A full-grown female guppy grows to a length of 3-6 cm (1.2-2.4 inches), while an adult male’s size is 1.5-3.5 cm (0.6-1.4 inches). Newborn guppy fry measure approximately 0.6 cm (0.25 inches), with both males and females reaching their full size six months after birth.

Diagram showing the difference in male and female guppy fish sizes.

Although guppies grow quickly, I recommend separating fry from adult fish to prevent them from being eaten by adult fish, including their mother.

Tank mates like kuhli loaches can also eat guppy fry.

You can return them to the tank once they grow to a size that won’t fit in the mouths of adult guppies (or other fish that can eat them).

When are guppies fully grown?

Guppies will reach the adult stage at six months of age. Their growth will either stop or slow down significantly. However, some male may still grow their fin and tail.

Guppies can live for 2 – 5 years but will become infertile when they reach an age of 1.5 – 2 years.

In the wild, male guppies can start reproducing at 1 month of age, but this can take a little longer in captivity. The fish reach their true sexual maturity at 3 months, especially those kept in aquariums.

On the other hand, female guppies reach sexual maturity at the age of 3 months. At this stage, female guppies appear visibly bigger than males, showing plumper, rounder bodies. However, mature males are more colorful than females.

Guppy species and their sizes

There may be slight variations in the size of guppy fish depending on their genetic makeup. Here are some varieties of guppies and their generalized average sizes.

Type of guppySize
Swordtail guppyUp to 5.5 inches
Blue delta guppyAbout 2.5 inches
Moscow guppyAbout 3 inches
Lyretail guppyAbout 2.5 inches

Moscow guppy and swordtail guppy fish are some of the biggest types of guppies in aquariums. 

Factors that affect guppy size

If your guppies aren’t growing to their full size even at a mature age, there’s something wrong that needs fixing.

Here are some factors that can affect the size of gup[y fish:


Guppies found in rivers and ponds are quite different from those kept in aquariums. The indigenous guppies are not very colorful.

The colorful guppies found in aquariums today have been bred by crossbreeding different species of guppies.

If the parent guppies are bigger, then the fries born will grow to a large size and vice-versa.


Guppies are omnivorous, meaning they can be fed on meat and plant diets. Their body requires nutrients such as vitamins, minerals, fiber, and protein.

Poor diet is one of the reasons why guppies grow slowly and attain their full size late. To ensure their nutritional needs are met to grow properly, provide sufficient food (but do not overfeed).

Feed them live foods, insect larvae, shrimp, veggie pellets, freeze-dried foods, soft algae, and blood worms.

Water parameters

Poor water quality is the leading cause of slow growth and even death in guppies. Guppies require a 72 – 84°F  temperature and a pH of 6.8 – 7.8. Failure to remove guppy waste and food leftovers from the tank will cause an ammonia spike.

A change in ideal water quality will cause the guppy to be stressed, affecting its growth.

Ensure a water temperature of about 80 degrees when your guppies are young and growing. At this temperature, the metabolic rate is great and your fish will grow at an optimum rate.

Tank size and stocking

Keeping too many guppies in a small tank will affect the water quality. The guppies will not have enough space to play, and they will deplete oxygen levels fast. 

Also, keeping guppies in a huge tank will affect their growth because they will use most of their energy swimming and looking for food instead of growing.

We recommend one gallon of water for every inch of guppy fish. For example, keep 2-5 guppies in a 5-gallon tank, preferably 2 females and 1 male.

Stages of growth

Guppies undergo four stages of growth to reach maturity. From the time they’re born, guppies will go through physical and behavioral changes and may have different needs at each stage.

Here are the four stages of growth in guppies:

  1. Fry stage: Since guppies are livebearers, they give birth to their young. The fry are tiny, fragile, and mostly translucent. They will spend most of their time hiding in the freshwater tank vegetation as they feed on infusoria (the microscopic/semi-microscopic organisms that live in fish tanks).
  2. Juvenile guppies: Juvenile guppies are about 3 weeks old. They’re clearly visible in the water, swimming actively since their tails and fins have started to grow. You’ll often observe juvenile guppies swimming together and schooling whenever they feel threatened. Juveniles can feed on small live foods such as daphnia and live shrimp.
  3. Young adult stage: The sub-adult or young adult guppies are about 2 months old but have not attained their full-grown size. However, they’re colorful with fully developed fins and tails. You can distinguish their gender because males will have developed the gonopodium (anal fin).
  4. Adult guppies: Guppies reach their adult stage around six months after birth. Most adult guppies will be about 2 inches in size, but their length will vary depending on gender and general health.


The size of adult guppies varies, but males are typically 1.5–3.5 cm (0.6–1.4 in) long, while females are 3–6 cm (1.2–2.4 in) long. However, selective breeding can and has produced guppies that may vary in shape, color pattern, and fin size.

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