Syntax:
set bmargin {<margin>}
set lmargin {<margin>}
set rmargin {<margin>}
set tmargin {<margin>}
show margin
The units of 5#5margin6#6 are character heights or widths, as appropriate. A positive value defines the absolute size of the margin. A negative value (or none) causes gnuplot to revert to the computed value. For 3D plots, only the left margin setting has any effect so far.
Normally the margins of a plot are automatically calculated based on tics,
tic labels, axis labels, the plot title, the timestamp and the size of the
key if it is outside the borders. If, however, tics are attached to the
axes (set xtics axis, for example), neither the tics themselves nor their
labels will be included in either the margin calculation or the calculation
of the positions of other text to be written in the margin. This can lead
to tic labels overwriting other text if the axis is very close to the border.