Misfit Animals is reader-supported. When you buy via links on our site, we may earn an affiliate commission at no cost to you. Learn More.

How Big Do Red-Eared Sliders Get? What You Need to Know

Full-grown red-eared sliders, that have been raised with plenty of space, can reach up to 12 inches. Males are smaller than females, only reaching 9 inches. Both diet, temperature, UV exposure, and habitat can affect their growth.

Red-eared sliders are arguably the most prolific pet turtle on the market. Their widespread distribution across the pet trade has caused them to affect local ecosystems all over the world.

The main cause for these invasive populations is irresponsible owners releasing or letting their sliders escape from their care.

It is critical for any current or prospective red-eared slider owners to know just how big your tiny turtle grows to be. 

This knowledge ensures you can take care of your turtle throughout its life.

Red-Eared Slider Size

Adult red-eared sliders grow to be 6–12 inches. Males average 6–9 inches, while females outgrow them at 8–12 inches. They are fully grown at approximately seven years old.

Red-eared sliders are small to medium-sized turtles. Both genders hatch the same size and grow at the same pace for the first five years of their lives. There is almost no difference between males and females during their juvenile years.

They begin to sexually mature at five years old. This is when females accelerate in growth, quickly overtaking the males’ size.

When fully grown, a male red-eared slider is 6–9 inches, while females are 8–12. This size difference is a key way to sex adults.

Red-Eared Slider Size

How Fast Do Red-Eared Sliders Grow?

Red-eared sliders grow quickly in their first year, reaching four inches when they are one year old. They then grow at around one inch per year until they reach full size.

When they reach sexual maturity at around five years old, the males slow in growth rate. Females continue growing at one inch per year until around seven years old, when they may be as large as 12 inches.

Red-Eared Slider Growth Chart

Stage Age Size 
Hatchling 1 month 1 inch
Baby  1 month–1 year 1–4 inches
Juvenile  1–4 years 4-8 inches
Adult 5+ years 8–12 inches

Why Are Female Red-Eared Sliders Bigger Than Males?

The size difference between genders of red-eared sliders is due to their different roles in reproduction. 

The female needs a larger body cavity to produce and carry clutches of 2–30 eggs clutches. Not only is she larger, but her overall shape is thicker and more domed.

In contrast, the male is smaller with a flatter shape. His size, coupled with the curvature of his plastron, enables him to mount the female with ease during mating.[1]

The male red-eared slider shell also features larger openings for its limbs between the carapace and the plastron. This allows for improved movement of his legs, which contributes to a successful courting of the female.

Larger males than females have evolved in animals where size is an advantage in male vs. male combat or forcible mating.[2]

Male red-eared sliders display neither of these behaviors so they have no pressure to grow larger than the females.

Related: Male vs. Female Red-Eared Slider: How to Tell The Difference?

Male vs Female Red-Eared Sliders size difference

How Long Till a Red-Eared Sliders is Full Grown?

Red-eared sliders are fully grown at approximately seven years old. They grow around 4 inches in their first year and a further inch per year afterward.

These pet turtles are slow to grow to their maximum size, not reaching their full length until seven years old. 

Hatchlings grow the quickest, measuring in at an average of 4 inches by one year. From one year onwards, they grow around 1 inch per each until they finish growing at seven years.[3]

Since females grow larger than males, their growth rate accelerates in the last two years. This boost to growth income from sexual maturity occurs around age 5.

Factors That Affect Red-Eared Slider Growth

Red-eared sliders need a suitable habitat, the proper environmental parameters, and a balanced diet to ensure a healthy and normal growth rate.

These average growth rates are standard for a healthy red-eared slider. Rates may vary in captivity based on the level of care provided by the owner.[4]

Factors that affect growth rate include:

  • Diet
  • Temperature
  • UV exposure
  • Habitat

Diet

Red-eared sliders are omnivores and sustain themselves in the wild on aquatic plants, insects, and small fish or frogs. 

The standard pet slider diet is vegetables, protein, and commercial turtle feed.

The diet changes as the turtle grows, with hatchlings needing high protein levels to fuel rapid growth rates. Juveniles need less protein and more vegetables as they grow, and by the time they are adults, they survive on 50% plant matter.

Related: What Do Red-Eared Sliders Eat?

Red-Eared Slider Diet & Feeding

Temperature

As ectotherms, red-eared sliders cannot thermoregulate internally. To power their metabolism and growth, they must collect heat energy from their environment. This is why temperature is vital for growth.

Water temperature 75°F–85°F
Basking temperature 85°F–95°F
Night temperature 65°F–70°F

UV Exposure

UV exposure is essential for digestion and the absorption of nutrients. In indoor enclosures, UV is provided artificially in the form of a UV bulb.

UV rays dissipate through the air, so the positioning of the bulb influences the exposure levels in the basking area. These specialized bulbs also lose effectiveness over time, so replace them annually.

Utilizing a solar meter (which measures UV index) can help turtle owners ensure they are providing the correct range of UV to facilitate their slider’s growth.

Habitat

The environment for a captive red-eared slider should promote all their natural behaviors. They need a large space with deep water and land-based basking areas with hides. 

Substrate, furnishings, and natural plants can stimulate a pet turtle, allowing them to stay physically and mentally fit.

Water quality must be excellent to ensure general health. Frequent cleaning alongside a good filtration system keeps the water safe.

Red-Eared Slider Appearance and Size

How Deep Should Red-Eared Sliders Water Be?

Red-eared sliders need water that is twice as deep as they are long. For example, a 4-inch juvenile needs a water depth of at least 8 inches, and a 10-inch adult needs a minimum of 20 inches.

Too much water can be hazardous to babies still learning to swim and prevent them from accessing basking areas. If the water level is too close to the top of the tank, red-eared sliders can climb out.

Water that is too shallow poses a risk to turtles. They may flip themselves over on their back and struggle to correct themselves without the resistance of enough water.

What Size Tank Does a Red-Eared Slider Need?

Red-eared sliders are highly active aquatic species and need large tanks to live happy healthy lives. For a juvenile under 4 inches, a 20–30 gallon tank is fine. As they grow, they require more space. A fully grown 10–12 inch slider needs an aquarium of at least 100 gallons.

Red-Eared Slider Health

How Big Do Red-Eared Sliders Get in Captivity?

Red-eared sliders in captivity grow to fully mature sizes of 6–12 inches when provided with adequate captive care, such as diet, habitat, and activity.

There is a common misconception in the reptile pet community that pet turtles only grow to fit their space. Many owners provide unsuitable small tanks for red-eared sliders, hoping they stay small.

This is untrue. The growth rate and size of a red-eared slider have nothing to do with its tank size. This rumor may have come to light by red-eared sliders receiving poor care alongside small spaces. 

This poor care, including insufficient nutrition and incorrect lighting and temperatures, is what really causes stunted growth in pet turtle species.

A properly cared for red-eared slider can grow to the same size as its wild counterparts. The captive setting does not have any influence on growth rates or sizes.

How Can You Tell a Red-Eared Slider’s Age?

You can tell the approximate age of a red-eared slider by comparing its size to a general growth chart. Their coloration can also be indicative of age.

No age technique deciphers your red-eared sliders’ age with exact precision. There are some methods to help make an estimate.

  • Size
  • Color 

To accurately measure your turtle’s size. Measure from the top of their shell down to the tip. The length measurement does not include their head or tail. Compare the length to a growth chart to estimate age.

Red-eared slider hatchlings under one year are vivid green, so quickly give away their age on observation. As they reach adulthood from 5+ years, their shells darken from green to dark brown. Males often get darker than females, appearing almost black from 7–10 years onwards.

Related: How Long Do Red-Eared Sliders Live?

How Can You Tell a Red-Eared Slider's Age

How Big is a 1 Year Old Red-Eared Slider?

A 1 year old red-eared slider is approximately 4 inches long. 

Between hatch their first birthday, red-eared sliders experience the fastest growth rate of their lives. To support this development, their diet is high in protein which is efficiently converted into energy for growth. 

Their metabolism will be higher than an adult and they will need to eat daily to maintain it.

How Old is a 2 Inch Red-Eared Slider?

A 2-inch red-eared slider will be between 3–6 months old. 

Red-eared sliders are 1-inch long when they hatch. By the time they reach one year old, they are 4 inches.  The 2-inch mark will be reached somewhere between 3–6 months depending on the health and activity of the individual.

Pet Turtle Size Comparison

Most pet turtle species are considered small turtles. Little turtles are preferred as pets due to lower space requirements. The range of sizes between pet species varies from 3 to 12 inches.

Red-eared sliders are amongst the most popular turtle species to keep as pets due to their adaptable nature. Even though they are considered small, in terms of common pet turtle species, they are amongst the largest.

Knowing how big your turtle grows is essential, as its size determines the amount of space it needs to be healthy. 

Red-eared sliders 6–12 inches
Spotted turtle 3–5 inches
Yellow mud turtle 5 inches
Musk turtle 3–4 inches
African side-neck turtle 7–12 inches
Eastern box turtle 4–6 inches
Yellow-bellied slider 6–12 inches
Northern map turtle 4–11 inches
Painted turtle 5–9 inches

Final Thoughts

Red-eared sliders are medium-sized pet turtles. Females reach sizes of up to 12 inches, while males usually do not grow beyond 9 inches.

Their size is larger than many other pet turtle species and as such sliders need extra space and care in captivity. Turtles need at least 10 gallons of water per inch of length, so a 12-inch female needs a minimum tank size of 120 gallons.

About Sophie Herlihy (Zoologist)

Sophie Herlihy, a trained zoologist, is a lover of true misfit animals. With a specialty in insects, birds, and rodents, she helps the Misfit Animals craft factual and valuable informational pieces on various animals.