How do you know if a turtle is a baby or adult turtle?

Well I have a pet turtle because i found it at the duck pond laying next to a tree and i think it is a adult because it is big but not the biggest and i think the way u figure that out is by the size but not always because along time ago, my cousin found a turtle at new braunfuels the size of my thumb and it was black and tiny. well and sometimes they don't grow by the looks but by the inside and years so it depends on what kind of turtle it is. I hope this helped! thank you for looking at my answer!

In most species turtles become adults at the age of 4-5. You can tell a turtle's age by the layers on the scutes. A scute is what makes a turtles shell look quilted. If you look closely at one then you should be able to see layers. If there are 3 layers than the turtles is 3, 4 layers then they are 4. It's not rocket science. In the wild turtles grow slower than in captivity because they don't get as much food and they burn more calories, so size isn't the best way to tell.