How Big Do Red-Eared Sliders Get In Captivity?

Red-eared sliders are popular aquatic turtles that can grow to the size of dinner plates! Find out more about their growth and care in the guide below.

In this guide, you’ll learn:

  • How big are red-eared sliders when fully grown?
  • How do you maximize the growth of RES?
  • What factors affect RES size?
Small, Medium, Large RES Turtles

How Big Do Red-Eared Sliders Get In Captivity?

LifestageAgeSize In Diameter
Baby Red-Eared Sliders3 months1 inch
Juvenile RES1-4 years4.5-5 inches
Adult RES5 years+8-12 inches

Red-eared sliders (trachemys scripta elegans) can grow up to 12 inches in diameter. They will grow depending on the environmental conditions they live in and is dependent on proper care, nutrition, and available space they have. 

The growth rate for red-eared sliders is not the same for all individuals and it depends both on physiological and environmental factors. In general, they tend to grow at a very fast pace for the first 5 years of their life. As they age, their growth rate decreases but maintains a steady rhythm until the age of 7 years. At this time, they reach their maximum size.

When cared for correctly, red-eared sliders in captivity can live up to 30 years and the biggest individuals can measure up to 12 inches or more. 

Depending on their size and age, red-eared sliders will have different space needs and nutritional requirements.

What Factors Affect How Big They Get?

1. Diet 

Red-eared sliders are voracious eaters. In their natural habitat, these reptiles have an omnivorous diet based on aquatic vegetation and small animals which they hunt to meet their protein needs. These include small fish, aquatic invertebrates, and tiny amphibians like frogs and newts. 

In captivity, mimicking such a varied diet can be a bit of a challenge, especially for new turtle owners. The diet of a red-eared slider in captivity should consist mostly of vegetables complemented with live fish, small amphibians, and insects.

📚 Read More >> Best Turtle Food For Red-Eared Sliders

2. Vegetables 

Vegetables should make up a big part of the diet of your red-eared slider, especially as it reaches maturity. This type of turtle loves dark leafy greens such as romaine lettuce, mustard greens, kale, green beans, collard greens, carrot tops, and Swiss chard. They also enjoy vegetables like carrots and bell pepper. Give leafy vegetables like spinach sparingly, as they contain oxalates that can interfere with their calcium absorption. Fruits, on the other hand, could give your turtle diarrhea so feed them these once in a while.

Vegetables that float allow your turtle to nibble on them during the day, providing them with the vitamin intake they need.

3. Insects and other live prey

Worms, earthworms, krill, crickets, and shrimp are good options to complete your turtle’s diet. They contain a good amount of protein, have little fat, and will make a tasty meal for your turtle. For smaller turtles, prey should be cut into smaller pieces.

Pro-Tip ⚡

Very young turtles will need a predominantly carnivorous diet. As they age, you should gradually introduce plants and vegetables. Older turtles do not need that much protein and their diet should be mostly vegetable or plant-based.

4. Fish 

Feeding live fish to your turtle can provide the mental and physical stimulation they need to keep their hunting spirit awake. Red-eared sliders are very strong swimmers and they will appreciate having to hunt their prey. Fresh fish also provides a strong calcium source for your pet, which they need to develop a strong, healthy shell and strengthen its bones. 

The nutritional requirements for red-eared sliders vary during their lifetime. During their first years, until they develop sexual maturity around the age of 5, they will need a higher protein intake. Growing requires a lot of energy for baby turtles and a rich caloric intake is crucial for their physical development. Their protein needs will gradually decrease during their life, with a predominantly vegetable-based diet at old age.

However, giving your turtle live fish too often can be very problematic for your pet’s health as it might lead to a vitamin B1 deficiency (thiamine) that causes a weakening of your red-eared slider’s defenses. 

Keep your turtle’s diet as varied as possible and don’t hesitate to consult a veterinarian if you suspect your pet might be suffering from nutritional deficiencies.

5. Space

The size your red-eared slider will achieve will also depend on the available space in its tank. Having an aquarium that is big enough for your pet to exercise and develop correctly is crucial to ensure the wellbeing of your pet and maximize its full growth potential.


The ideal tank size for a red-eared slider should be at least 4 or 5 times the size of your animal’s carapace. Red-eared sliders are very active swimmers, so they benefit from having a big tank where they can exercise with ease.

A baby red-eared slider can start its first year in a 30-gallon tank. As it grows into a juvenile turtle (measuring around 6 cm), it will need at least a 55-gallon tank. A fully grown 11-inch slider will need an aquarium which is at least 125 gallons to lead a healthy and happy life. 

📚 Read More >> Best Tanks For Red-Eared Sliders

Bigger tanks can also help ease the workload of your filtration system as turtles can get quite messy. Having clean water in their aquariums at all times prevents illnesses due to infections especially due to the common bacteria, salmonella.

6. Gender 

The gender of your pet is also a determining factor for its size. Although during the first months of life, both female and male sliders present the same size, sexual dimorphism starts showing up when they reach sexual maturity around the age of 5. From that moment on,  female sliders often become bigger than males. This difference in size makes it easier for red-eared sliders to mate during the breeding season. 

How Big Are Baby Red-Eared Sliders?

Baby red-eared sliders are very small and that is partly why, along with their friendliness and adaptability, they make such popular pets. During the first 3 months of life, they are only around 1 inch in diameter and weigh less than 60 grams. However, baby red-eared sliders will increase enormously in size and weight during their first years of life.

How Big Are Juvenile Red-Eared Sliders?

Juvenile red-eared sliders still have a long way to become adults. Normally at the age of 4 years, they measure around 4.5 inches. They will keep on growing at a slower but steady rate, around 1.5 inches a year until they reach their adult size.

How Big Are Adult Red-Eared Sliders? 

We consider red-eared sliders to be adults from their 5th year of life, a moment in which they reach sexual maturity. However, at the age of 5, it is very probable that your pet still has a few inches to grow until they are about 11-12 inches which is typical for adult turtles. Male sliders are slightly smaller in size than females, normally measuring around 8-10 inches. 

During adulthood, red-eared sliders will grow at a much slower pace than baby and juvenile sliders. They normally stop growing at the age of eight. 

Regarding weight, a fully mature female red-eared slider can weigh up to 550 grams. Males are smaller and lighter than females, so their average weight is around 250-300 grams.

When Are Red-Eared Sliders Fully Grown?

Red-eared sliders are fully grown at the age of 8, the age at which they reach their maximum size and weight. 


Red-eared sliders can grow as big as 12 inches (30.5 cm) when given the proper care, especially during their growth years. They grow up to 3 inches in their first year and then an inch per year after that. Their maximum growth rate in captivity is affected by factors such as genetics, nutrition, and habitat. Make sure you have a big enough tank with the proper setup equipped with filters, UVB lighting, and a heating lamp. This allows you to provide the best care for your slider to help maximize its growth potential and ensure its good health. 


How fast do red-eared sliders grow?

The growth rate of red-eared sliders will vary from animal to animal. If fed correctly and given proper living conditions, a red-eared slider will increase its size by 2 inches during the first year. From the 3 years on, their growth rate will decrease but their size will keep on increasing around an inch per year until they reach maturity.

You can make sure the growth rate of your turtle is adequate by using a chart that shows the relationship between the age and size (length) of red-eared sliders. 

How big do baby red-eared sliders get?

Baby red-eared sliders are very small. In the first months of their life, they are no bigger than 1 inch in length. During their first years, they will increase in size considerably, growing at a rate of 3 to 4 cm in the first year and then growing steadily around 2 inches every year. From the moment they reach sexual maturity, their growth rate will slow down. In these cases, you will see sexual dimorphism in your pet. If it’s a male red-eared slider, it will be smaller than its female counterparts.

How big is a 1-year-old red-eared slider?

A 1-year-old red-eared slider will measure around 1.6 inches long. 

How can you tell the age of a turtle?

Determining the age of a turtle is not an exact science, however, some tricks will help you estimate the age of your pet easily. Counting the rings on its scute and comparing the size of your turtle with others from the same species can give an estimate of age. Observe the rings on the scute of your animal’s carapace and count them. Then divide the result by two.

Another method is growth. This works particularly well in young individuals as they grow at a more defined pace. Measure the length of your turtle from the tip of its shell to the end then compare the results with a growth chart for their species. 


Facts on the Red-eared slider:

Red-eared slider (Wikipedia)

Red Eared Slider (Wildlife Facts)

Fact sheet on the RES specific to its distribution in the US:

Red-eared Slider (Trachemys scripta elegans) – Species Profile

Care guides:

Red-Eared Slider Care: Diet, Habitat, & Characteristics

Informative subreddit for owners and enthusiasts:

Red Eared Sliders – Owners and enthusiasts!

Lara Sotto

Lara Sotto

Lara Sotto is a marine biologist, freelance animal writer, and reptile lover. She is passionate about empowering reptile owners with the information they need to give the best care possible for their reptiles. She is currently taking up her Ph.D. in Marine Science and providing her knowledge to the ReptileKnowHow community.

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Lara Sotto

Lara Sotto

Lara Sotto is a marine biologist, freelance animal writer, and reptile lover. She is passionate about empowering reptile owners with the information they need to give the best care possible for their reptiles. She is currently taking up her Ph.D. in Marine Science and providing her knowledge to the ReptileKnowHow community.

About ReptileKnowHow

We’re a team of reptile owners and experts who are on a mission to share practical, science-based tips and recommendations to other reptile owners.

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