Not JBTexas but you have to measure the area for each zone. You also have to know the flow rate of your sprinklers in each zone (total flow in gpm when the zone runs). Then use the calc above. If you want to know where the formula comes from then check here: How do I calculate my precipitation rate?
Note that when you tell Rachio the brand of nozzles that you have, it will default to specific precipitation rates. If you have Hunter MP Rotators, it defaults to 0.8 in/hr. Most MP Rotators are actually 0.4 in/hr. Anyway, if your system is designed for head to head coverage, your precipitation rate will be greater than the default sprinkler head value because the area will be watered by at least 2 heads if not more depending on system design. This is one reason why the 2 values need to be determined and a value calculated.