Calculate How Much Space Text Will Take Up?

I want to dynamically resize textareas to always have enough rows to hold the data, so there is never a need for a vertical scroll bar no matter whether the user types in large paragraphs or only puts one character per line. Is there some kind of existing facility for doing this? Perhaps in a library? Or maybe there is a property of the textarea which can be checked in a row-incrementing loop to determine whether a scrollbar is still needed.