How do you arrive at the correct ARV

[Alan Russell]

Does anyone use price per square foot when calculating ARV?

[J Scott]

No.  There are too many other factors -- location, condition, layout, neighbors, etc.

Note that a CMA often won't give the the right answer either -- it will simply indicate where the appraisal should come in. Which is not necessarily what a buyer would be willing to offer.

Find a great agent who is intimately familiar with the area and get their opinion of value.