I am a lot like Goldpro, on the normal residential it is either $30,40 or 50. On the larger commercial accounts I time myself while walking the parameters and around buildings and drives. The time it takes me to walk the major lawn is a multiplier on lawns I already mow. example (12 min to walk = 48 min to mow) @ $1. per min mowing charge = $50 charge.
This system give me the best real time estimate on mowing around many buildings large obstacles, drives ways and side walks.
This is also a real application of the equipment I use, because I have timed both walking time a driving time on lawns I do now. So it is personally applicable.
Same for much bigger lawn, 28 min to walk = 112 min mowing time =$115 charge. works for me..
A wheel measurement is ok, but takes as much more time and has no effect on time to mow said sq foot. Great for fertilizers for sure.