question on measuring for a replacement window

hi
i am measuring for replacement windows- i understand how to measure for the height but the width if a question-- my existing window has a plastic glider system, spring loaded- so when i am measuring for the width do i only measure from glider to the other glider or do i take the gliders out and measure ( i believe adding one total inch to the width)- do the gliders come out when i replace the window -- these are wood windows and i am replacing with vinyl
thanks
bob

Measure to the inside edge of the interior stop and deduct 1/4" from the width to give you 1/8" on either side to shim and square up.

The plastic jambliner will be going away when you are pulling out the old window.