An octave is always 8 white keys and 5 black keys.
There are 7 octaves on a standard grand piano (plus a minor third, or one additional "black key"). If each octave has 5 accidentals (or black keys) then 7 octaves would have 35 black keys, plus the additional B Flat at the bottom of the piano.....so: A 72 key piano has 36 black keys.
A 128-key piano has 128 keys.
An 85-key piano has 85 keys.
There are 61 keys on a standard 61-key piano keyboard.
In an Octave or Perfect Eighth, there are 12 ( 13 if you count the eighth). For scales that begin on white keys, there are always 8 white keys and 5 black keys in a single full octave. For scales that begin on black keys, there are always 6 black keys and 7 white keys in a single full octave.
Take any key of the piano and count 12 keys (whites and blacks) to the "right" or to the "left". The 12th key is an octave higher or lower to the initial key.
88 Piano Keys
88 keys on full size.
Mon-keys Don-keys Piano keys
The key that uses all black keys on the piano is the key of D minor.
52 keys on a standard 88-key piano are white, 36 are black.
88 Piano Keys on a KeyBoard