Hi , it's about as big as my hand they are a herbivore so shouldn't eat the tetras also if you have a shoal of small fish the dollar tend to leave them alone as the see them as one he is so placid its unreal thanks for your comment what fish do you have?
Nice silver dollar Be aware that they can reach about 7". 100g tank or so is perfect for them. They are schoolers and should not be kept alone. Even if you can get a whole school, I would have no less than 4.
Some silver dollars will kill small fish like neons. Some don't.