You must set a fixed right margin with e.g. set rmargin at screen 0.85
. That sets the right border of the plot at 85% of the image size:
set multiplot layout 3,1
set rmargin at screen 0.85
plot x
plot x
plot x linecolor palette
unset multiplot
set output
Output with 4.6.3:
See also the related question multiplot - stacking 3 graphs on a larger canvas.
Generic solution for fixed margins
If you want a layout with one row and three columns, can use the multiplot
options margins
and spacing
to get three plots which have the same width:
set xlabel 'xlabel'
set ylabel 'ylabel'
set multiplot layout 1,3 margins 0.1,0.9,0.1,0.95 spacing 0.05
plot x
unset ylabel
plot x
plot x linecolor palette
unset multiplot