Growing and need help

[SullysAllSeasons]

So I have been doing lawns for about 7 years now,5 as a side gig 2 full time, and I am trying to grow into larger residential and commercial properties. I have never really had to figure out how much ground my mower can cover in a certain amount of time as residential properties around here are all between 30-40 dollars. Anyway I want to buy a 60" zero turn for a few properties I have had my eye on if I get them. So long story short how the heck do I figure out how much ground I can cover with that size, or any size for that matter, mower so I can attempt to bid on some of these properties? Your help is appreciated. Thanks!