The professional level of piano is 47″-49″ tall. In metric, this piano size often denotes the model. For example, a model 121 is 121 centimeters tall or 48″ tall. What makes a professional sized piano? There are good reasons for playing a professional piano (see our Article on Why Upgrade to a Professional Level Piano) but generally, it’s a combination of having a full sized action with substantial length in piano strings. While the studio sized pianos often have full sized actions, they don’t deliver as much depth of tone. Consoles have both shorter strings as well as ‘compressed’ actions. When you arrive at the professional level, generally there are longer keys and a full-sized action as well as a richer tone due to string length. Just because a piano is professional size, it does not speak to the quality of piano. Pianos still vary from brand to brand, model to model. Doing your research on what piano to buy is always prudent.
For more information on piano sizes, please refer to the Piano Price Point article Piano Sizes ~ What Should I Buy?