The Encyclopedia Britannica states that the standard number of keys on a modern piano is 88. A piano with that number of keys has a compass, or range of notes, of seven complete octaves plus a few keys.
The piano's sound emerges when its wire strings are touched by the felt-covered hammers that are moved by pressing a key on the keyboard. The use of felt to cover the hammers is a modern occurrence as in the past, leather was the material of choice. Modern pianos are a great deal louder than 18th-century pianos because the frames of pianos are now constructed of cast iron as opposed to wood.