Why acreage alone is a bad pricing unit
An acre of light, grassy fuel and an acre of dense, mature blackberry or manzanita are wildly different jobs — the second can require many times the animal-hours to clear thoroughly, even though both are "one acre" on paper. That mismatch is exactly why sight-unseen, flat per-acre pricing is unreliable, and why professional operators think instead in goat-days: the amount of vegetation one goat eats in one day of grazing.
Project planning works backward from that unit: an estimator assesses vegetation density and type, estimates the total goat-days a site requires, then divides that total by however many goat-days are available per day (herd size) to land on a project duration — or works the other way, sizing the herd to hit a client's deadline.
What actually moves the number
Density and woodiness are the biggest swing factors — light annual grass might take a fraction of a goat-day per acre, while dense, mature brush can take many goat-days for the same footprint. Terrain and access matter too: steep or broken ground slows grazing pace even when vegetation density is similar to flat ground, because animals move and browse less efficiently on a slope.
This is the technical version of something every experienced herder already knows instinctively from walking a site: the number that actually determines cost isn't how big the property is, it's how much total plant material has to be eaten, and how hard the terrain makes that work.