What size do red eared slider turtles lay eggs?

An fully grown adult will have an upper shell (carapace) up to 10 inches in length.
Red Eared Sliders get to be 10-12 inches long. Females will grow to be larger than males.

Red eared sliders can get up to 8in to 10in for males and 10in to 12in for females

It takes 5 years for them to get fully grown, in captivity. They can get anywhere from 10-12 inches & they live for about 40 years. Make sure you have at least a 100 Gal. tank or a small outdoor pond for your full grown slider.

Also, they must have a heat lamp of at least 60 watts, located above their land, so that they can have a place to bask. You will need a water heater that will keep the water temp from 75-80 degrees F. Keep a thermometer in the water to ensure that the temperature is staying constant. The basking place should be 80 F - 85 F.

~Annie De..., Future owner of Pet Love.

Revised and corrected by Maddie Moo
Red Eared Slider turtles get to be 10-12 inches long, females being bigger than males.
Adult red ear turtles reach up to 25 cm (10 inches) in carapace length.
i have heard anywhere from 5 to 12 inches
well they will get as big as you let them, if your have a small aquarium, they will stay relatively small. A big tank (like 50 or 60 gallons is recomended) they will reach their normal, and healthy size. a small tank is really cruel. they will get up to 12 inches at top, healthy size. 10 gallons per ich is healthy. a healthy turtle is alot more active, fun to watch, and most of all worth your money!

I have seen red eared sliders (females) as big as sewer lids. This is not an unusual size in the wild. I often saw them this size by the river and lake on our farm. So, it depends on how big your tank is and if you have males or females. In my experience, they will continue to grow larger and you will need to provide quite a large tank for them. They are quite messy, like all aquatic turtles, so know what you are commiting to before you get them. They are rewarding animals if you are willing to put in the time, space and effort!