Question: how big are piano keys?
Answer: Modern piano keyboards ordinarily have an octave span of 164–165 mm (6.5–6.5 in); resulting in the width of black keys averaging 13.7 mm (0.54 in) and white keys about 23.5 mm (0.93 in) wide at the base, disregarding space between keys. Several reduced-size standards have been proposed and marketed.