Bluebulb Projects' The Measure of Things presents:
50 is about three-fifths the number of Keys on a Piano.
In other words, it's 0.57 times the count of Keys on a Piano, and the count of Keys on a Piano is 1.8 times that amount.
(Moden layout; A0
Most modern keyboards have 88
keys, comprising seven octaves and an additional major third. A full-size, acoustic piano may have as many as 12,000