it depends.some have 52,some have 85.they vairy because the country they are made in is different,the makers are different,the model for the purpose is different.i dont think its a one word answer,sorry. :P
Well, I've been taking piano lessens for 8 years, I'm 11, so, yeah, but I've learned that with the different types of pianos; baby grand, concert grand, all those, the number of keys vary. It would depend on what kind of piano you were asking about! Hope it helps!