Unveiling the Growth of a Red-Eared Slider: Age & Size Chart

Tanja is a qualified postgraduate scientist with a great passion for nature and how different ecosystems interact. Her education included coursework and practical experience to advance in biological sciences, farming, aquarium research and fisheries management. She has experience in constructing ponds, aqua- and hydroponics, productive gardens with a small worm farm and compost heap, and larger scale mariculture facility setups.

There is a common misconception that all red-eared slider turtles are the same size. Such a statement could not be further from the truth!

The size of a red-eared slider turtle can vary significantly based on the gender, food, and environment of the turtle. Why is it important to know about the size of turtles? Not only does the size provide valuable information about an individual, but it also helps you plan your enclosure better, keeping future turtle growth in mind.

Keep reading to find out everything you need to know about the size of red-eared sliders, which will guide you in choosing your next turtle friend(s).

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Captive bred versus the size of wild red-eared sliders

There are a few things to consider when you look at the size of your red-eared slider. The first is whether you want a captive-bred or wild-caught turtle. While both can make excellent pets, there are some differences between the two that may make one more suitable for you than the other.

Captive-bred red-eared sliders are typically smaller than their wild-caught counterparts. For those in captivity, it is because they are bred in captivity, and their growth is carefully monitored and controlled. As a result, captive-bred red-eared sliders will reach a smaller adult size than if they were left to grow on their own in the wild.

However, wild-caught red-eared sliders can vary greatly in size. Some may only grow to be a few inches long, while others may reach over a foot in length. This is due to the fact that they are not kept in captivity, and so their growth is not as controlled. Both captive-bred and wild-caught red-eared sliders have the same biological form.

If you are looking for a turtle with a specific size or average lifespan expectancy, then it is best to go for a captive-bred one. However, if you do not mind what size your turtle grows to, then a wild-caught red-eared slider may be more suitable for you.

That said, regardless of the size of the red-eared slider when you get them, if the individual is adequately cared for with the most optimal conditions, they can get as big or even bigger than wild-caught red-eared sliders.

Male versus female red-eared slider size

In general, red-eared sliders are smaller-sized aquatic turtles compared to other common turtles. They are, however, amongst the largest slider species in the slider turtle family. When red-eared sliders hatch, both genders are similar in size and grow steadily at the same pace for at least the first four to five years as juveniles.

The moment sexual maturity has been reached, more or less at the age of five, the growth of females accelerates for two years and exceeds male red-eared slider sizes. At this point, they can weigh between three and six pounds.

Female red-eared slider turtles are typically much larger than their male counterparts. A female turtle’s shell can grow to be up to 18 inches long, while a male’s shell usually tops out at around 12 inches. The average size of adult male red-eared sliders is between six and nine inches, whereas females outgrow the males by an average of eight to 12 inches.

So why the difference in size? It turns out that the size of a turtle’s shell is directly related to its reproductive success. The larger the turtle, the more eggs it can lay. As a result, females require a larger body cavity, enabling the female to produce and carry clutches of two to 30 eggs.

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Red-eared sliders at Virginia Lake, September 2021. Photo / Ormond Torr

Since males do not lay eggs, they do not need to be as big as females. Visually, the males will be smaller than adults with a flatter shell shape, whereas females are larger and more dome-shaped. The tails of male red-eared sliders are far thicker and longer than those of females.

However, it is advantageous for males to be smaller in size yet have larger openings for their limbs, which assists in a successful courting encounter with the female.

So if you are considering buying a red-eared slider turtle, make sure you know which sex you are getting! Otherwise, you might end up with a turtle that is much larger (or smaller) than you were expecting.

How to tell a turtle’s age by their size

Though there are a number of methods you can use to decipher your turtle’s age by size, please remember that this is not precise and only provides an estimated age.

The most common method to find out your turtle’s age is by measuring the individual’s shell and looking at their shell’s color. This information is then compared to a general growth chart that indicates the red-eared slider’s approximate age.

Firstly, measure your red-eared slider’s shell from the top (head side) and all the way down to the tip (tail side). Secondly, compare the measurement to the general growth chart to get an estimated age of your slider.

A less accurate way to determine a red-eared slider’s age, instead of measuring the shell, entails looking at the turtle’s shell color. For example, a vivid green shell will be indicative of a red-eared slider below one-year-old. Whereas the shells will darken as red-eared sliders age, becoming a dark brown by the age of five. The shells of female red-eared sliders above the age of seven have the tendency to go so dark that the shell appears black.

If you only want an approximate estimation of your red-eared slider’s age, you can use a size timeline in conjunction with a growth chart. Please see the section below on how to go about this method of determining turtle ages.

Size timeline and growth chart

Hatchling: A red-eared slider hatchling around the age of one-month-old is approximately one inch in size, growing at a rate of four inches per year. Thus, a slider should be around two inches between three and six months old.

Baby: The red-eared slider babies that are older than one month, and up to one-year-old, average at 1.5 to four inches in size. When the babies reach the age of one year and are close to four inches in size, the growth rate slows down to one inch per year.

Juvenile: A juvenile red-eared slider between the ages of one and four years is approximately 4.5 to eight inches big, growing at a rate of one inch per year.

Adult: The red-eared sliders have reached maturity as an adult when they are any age above five years. Their sizes can range between six and 12 inches based on their gender, environment, and diet or food availability. No further growth occurs around the age of seven.


Stage of life cycle


Size (Approx)

Hatchling0-1 month1 inch
Hatchling/Baby1-3 months1.5-2 inches
Baby3-6 months2.5-3 inches
Juvenile1 year4-5 inches
Juvenile2 years5.5-6 inches
Juvenile3 years6.5-7 inches
Juvenile4 years7.5-8 inches
Adult5 years8.5-9 inches
Adult6 years9.5-10 inches
Adult7+ years11-12 inches (Max)

Factors that affect red-eared sliders’ growth and size

There are many factors that affect the size of red-eared sliders. Some of the most important factors include:

The age of the slider: Younger sliders tend to be smaller than their older counterparts. Refer to the general growth chart for more information on the age of the red-eared slider turtle specific to the size.

The environment: Sliders that live in wilder, more naturalistic environments tend to be larger than those that live in captivity. This is likely due to the fact that these red-eared slider individuals have more space to roam and grow in the wild. The following related environmental parameters are essential to red-eared slider growth:

  • Habitat: A suitable habitat should be as close to a simulation of a red-eared slider’s natural environment. Hence, ample space with sufficient water and a basking area with hides will all promote healthy growth in your sliders.
  • Temperature: Heat energy, obtained from their surrounding environment or installed heat source, is required to thermoregulate red-eared sliders’ metabolism and growth.
  • UV exposure: Either natural sunlight or a UV bulb assists with nutrient absorption and healthy digestion in red-eared sliders, which allows for optimal growth.

IMPORTANT NOTE: Your red-eared slider(s) will not stop growing because you put them in a smaller enclosure that only allows them to grow according to the space available. Instead, this results in poor and cruel care on the owner’s behalf!

Diet: A slider’s diet can also affect its size. The red-eared slider individuals that eat a lot of protein tend to grow larger than those that do not.

If a red-eared slider’s habitat is not suitable with the appropriate environmental parameters, and they do not get a healthy, balanced diet with all the nutritional value, their growth will either be much slower or even be abnormal.

Final thought

Make sure you have the space to house a red-eared slider comfortably for the sizes they can grow up to and have the time to provide adequate care for the optimal growth of your pet turtles. Your red-eared slider turtles have the potential to grow and live long, healthy lives accordingly.

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