In Season 1, Edward was depicted as a little engine. From Season 2 on,he was no longer called "little Edward". Do you think Edward is a small engine? They say James is a big red engine but he's the same size as Edward, so are Edward and James small engine or big engines?
I know James was sometimes called big, and sometimes called small. It's confusing.
In Edward Helps Out, right at the beginning of the episode, the narrator says "They were all bigger than Edward." Uh... Thomas was there.
James and Edward are roughly the same size as each other with James being a little bigger, as far as the tender engines go they are considerded abit small as they aren't Gordon or Henry's size, but they are still bigger than say...Thomas or Percy :).
Hope this helps :).
Interesting question, especially because you can look at it several different ways. For instance, the engine's size could be determined by something like wheel arrangement, weight, length, hight, etc. I'd say he's small, just because his build is slightly smaller than all the other tender locos, even the Scottish Twins by at least four long tons.