Red-eared sliders grows in three phases. Baby turtles are more miniature than juveniles, which are also smaller than adults. However, a mature red-eared slider can grow to the size of a plate. A grown adult turtle will measure between 8 and 13 inches in diameter. However, the male red-eared sliders will be slightly smaller than the females for breeding purposes.
The male and female turtles are usually the same size in the first five months of their lives. At three months old, baby red-eared turtles will have a one-inch diameter. As they age, the male and female red-eared sliders start showing sexual dimorphism. Unlike the larger females, the adult male red-eared sliders reach 5 to 9 inches.
The baby and juvenile red-eared sliders grow faster than the adults. The young turtles add about 1 to 1.5 inches every year. But the turtle’s size depends on its genetics, habitat, and nutrition. I’ve discussed below how big red-eared sliders can get. You will also find a size chart by age and learn how long it takes the red-eared slider turtle to grow to full size.
What is the average size of a red-eared slider turtle?
The size of an adult male red-eared slider turtle is 5 to 9 inches. The female red-eared slider is much bigger and will grow to a diameter of 8 to 13 inches. Therefore, the average size of a red-eared slider turtle is about 6 to 11 inches.
You can even tell the age of a red-eared slider turtle using its size. If you don’t know how old your turtle is, measure its length. Put your turtle on a clean piece of paper. It will retract into the shell. Use a pen to mark the paper directly in front and at the turtle’s rear end.
Return the red-eared slider turtle to the tank. Measure and record the length of your tortoise in inches. Use the size chart by age below to know your turtle’s age. For instance, a 6 to 8 inches red-slider turtle is about 5 to 7 years old.
The average size of red-eared slider turtles is nearly the same in captivity as in the wild. Perhaps the only significant difference is their weight and lifespan. The male and female red-eared sliders will weigh up to 300 and 550 grams, respectively. However, the turtles will live only 20 years in the wild and up to 40 years in captivity.
Note that the red-eared slider’s size, weight, and lifespan depend on various factors like nutrition, genetics, and habitat.
Red-eared slider nutrition
They love eating dark leafy greens like collards and small aquatic animals like daphnia. A balanced diet for your red-eared sliders has essential fats, proteins, vitamins, and minerals to ensure optimal health and growth.
Red-eared slider habitat
You should give the turtle enough space to facilitate its growth and development. Give the red-eared turtle 10 gallons of water for every inch of its shell length. However, keep the minimum tank size for red-eared sliders at 50 gallons.
Red-eared slider genetics
Although it can be challenging to know your turtle’s genetics, it plays an essential role in the turtle’s size. The easiest way to know how big your red-eared turtles will grow is by looking at their parents. The baby turtles are more likely to be the same size as the parents because they share a large part of their genes.
How long does it take for a red-eared slider to grow full size?
Red-eared sliders can extend to full size in 8 years. The red-eared slider turtles will stop growing once they reach that age or grow at an insignificant pace.
On the other hand, young and juvenile red-eared sliders grow pretty fast.
Also, between zero and three months, the red-slider turtles will grow much slower than the juveniles. It is worth noting that juvenile turtles are between one and four years old. At that stage, red-eared sliders eat more and are more active than the adults and the baby turtles.
Juvenile turtles measure between 4.5 and 5 inches. Their growth rate is also quite significant. For instance, the young red-eared turtles will grow by 1 or 1.5 inches for the following years of their lives until they reach adulthood.
However, if the turtle tank conditions are unfavorable, your red-slider turtles can stay stunted longer than usual. If you’ve had your turtle for more than four years, for example, and it is less than 3 inches long, then something is not correct.
Size chart by age
The 1 to 4-year-old juvenile red-eared turtles will be between 4.5 and 5 inches long. And finally, your adult red-eared sliders will reach between 8 and 12 inches. However, some fully grown female red-eared sliders can reach 13 inches. But that’s not very common.
As I said earlier, give your red-eared sliders high-quality nutrition and enough space. But most importantly, change the turtle water at least once a week.
I also recommend installing a turtle filter in your tank to improve water filtration, lessen the stress, and encourage the healthy growth of your red-eared slider turtles. In that case, your baby red-eared sliders will reach about 1 inch within three months.
Below is a table summarizing the size of the red-eared sliders by age:
| Red-eared slider turtles | Age (years) | Size |
| Babies | ¼ (3 months) | 1-inch |
| Juveniles | 1 | 1.6 inches |
| 2 | 4 inches | |
| 3 | 6 inches | |
| 4 | 7 inches | |
| Adults | 5 | 8 inches |
| 6 | 8-10 inches | |
| 7 | 8-11 inches | |
| 8 | 9-13 inches |
Male vs female red-eared slider turtle size
There are several differences between male and female red-eared slider turtles. However, sexual dimorphism is only noticeable in the juvenile stages. That is when the turtle is one year old and above.
The most common difference between male and female red-eared sliders is size. The turtles are usually the same size in the first five months of their lives. However, as they age, the females will get slightly more significant than the males for breeding purposes.
A mature female turtle will measure between 9 and 13 inches in diameter. Unlike the larger females, the adult male red-eared sliders reach 8 to 11 inches. Note that their size difference can be 1 or 2 inches. However, a few red-eared slider turtles will get to 13 inches long.
Researchers Berry and Shine say that male turtles are smaller than females to increase their mobility and ability to locate the females. The size difference also makes it easy for the males to climb and mate with the females.
Another way to distinguish between the male and female red-eared sliders is by observing the curvature of their plastron (belly shell). The plastron is curved inwards in the males and slightly outwards in the female turtles.
The curved plastron is visible when the turtle is one or two years old and above. It allows the male to mount the female red-eared slider and form a firm grip. In other words, the male red-eared slider will not fall off the back of the female during intercourse.
Here is a table for the size of male and female red-eared slider turtles:
| Red-eared slider turtle | Size (diameter) |
| Male | 8 to 11 inches |
| Female | 9 to 13 inches |
References
- Berry, J. F., & Shine, R. (1980). Sexual size dimorphism and sexual selection in turtles (Order Testudines). Oecologia, 44(2), 185-191.
- The Tortoise Table. (2017)