You mean as a chord? It depends on the particular pianist's finger geometry, but also, the span of notes depends on the bottom note -- sometimes you can't reac

You mean as a chord? It depends on the particular pianist's finger geometry, but also, the span of notes depends on the bottom note -- sometimes you can't reach that black or white key, and note that the black keys aren't exactly in the middle of the white keys, so the distance changes. The span from B to D flat is easier than that from C to E flat. Also, one finger can press multiple keys. For example, this is necessary to play three FGDF/FGDG chords in Chopin Op. 10 No. 12.