Question

Certain emacs function splits the current frame, for example magit-status or compile (probably there are dozens). How emacs decides whether to do a vertical split or a horizontal one?

My experiments suggests that if the frame’s width is larger then 162 chars then it dose a vertical split, and otherwise a horizontal one. Is it the right value? More important, where is this value stored, how can I change this threshold?

Answer 1

split-width-threshold:

Minimum width for splitting windows sensibly. Hide If this is an
integer, split-window-sensibly may split a window horizontally only
if it has at least this many columns. If this is nil,
split-window-sensibly is not allowed to split a window horizontally.

Standard value is 160 here, looks pretty close to what you’ve found.