speaker width

I am wondering if people use the side of cabinet or center of cabinet to determine speaker width apart.I guess its time to really dial it in and would appreciate input.
Front center. For just trying raw data places.. i use fractions. ODD fractions. Measure the room. start cutting it up by thirds, fifths, sevenths, for 'crazy things like partial walls which makes everythiing more complicated, check both measurements.
Try to NOt allow one measurement to be an EVEN fraction of another one with these partials. Especially say a window well is a fourth from the speaker,when the wall itself is thirds...
I know you did not ask that stuff, but i volunteered it anyway.
Speakers on end of long rooms often work well at sevenths front to back with fifths across: that is one fifth from each side wall, and three fifths in-between.
This is ONE way to start, others exist.
thanks liz,im just trying to dial it in after a year of having them situated.lots of ways to try but i do have a open back wall to kitchen??thankyou.
Center of woofer.
It doesn't matter where you measure from.