OK, I wanted to compute the time needed to cut my back yard... thus finding the formula needed for my mower. I walked off the back yard using my Lufkin rolling tape measure... I guess that's what you call it. This gave my my back yard in sq ft. So: SqFt of my back yard = 12768 1 sq foot = 2.29568411 × 10^(-5) acre Backyard sqft * 2.29568411 × 10(-5) acre = .2931129472 (this is the total acres of the back yard) mph of mower = 2.0 cut width = 42 acres cut per hour (at 80% efficiency) = ((mph*cutwidth)/120) so... ((2.0*42)/120) = .70 acres per hour Time it takes to cut back yard = (back yard acres/acres per hour) so... (.29/.70) = .42 hours to cut back yard so... .42*60 = 25 minutes to cut back yard. Is that right???? Now, don't ask me to cut the back yard and time it!