We price a job by window counting, and it seems to work, no matter which window cleaner we work with, a standard 2 pane window can be anything from 50p per window, right up to £2 in chiswick!
So at the £1 rate, a 2 pane 'standard' window is £1, a 3 pane window is £1.50, 4 pane £2, patio door, £1.50-£2 ea, small windows, 50p.
It is much easier to do the counting of windows first, then just multiply by the rate per window you are prepared to work at.
Paul