Is there a standard length and width for piano keys?

This is a very good question. Generally, American pianos have slightly shorter keys than Asian pianos. Some older pianos had even shorter keys. In addition, the length and width, as well as the angle of the slope on black keys varies on pianos - particularly on older instruments. read more

There is no single textbook standard that is rigorously followed by all manufacturers. That being said, key width on modern grands and uprights doesn’t vary much in practice — it’s generally about 10–11 mm for the black keys, and 23–24 mm for white keys. These measurements are at the “key head,” which is the end nearest the player. read more