Avery is 100% correct. The irrigation contractor should not bid on the job untill you know: (1) meter size (2) size of the line into the house and past the meter, this is usually the limiting factor. (3) length of the run, pressure loss through friction (4) static, and if possible dynamic, pressure The only way to bid a job without the above is, if you are on city water, bid on the minimum reqirements for main, meter and pressure reqired to meet code. Example: For the purpose of this example the main line into the house is the limiting factor and the head total = 40gpm with 2gpm heads, we will assume 0 pressure loss from friction. 1) 3/4" main. Since the velocity cannot exceed 5 fps you could only put 4 heads/ zone, or 8gpm/zone, this would mean you need 5 zones. 2) 1 1/4" main. you would need only 2 zones.