Enter Painting square footage to calculate gallon coverage or add up square footage by walls or room. This will tell you how many gallons of paint you need for your next paint job. Save your Interior and Exterior Painting Estimates, Invoices, Customers, and Jobs. Save your Item Prices in settings and add up your painting estimate. Estimates and Invoices can be sent by email directly from app. also add up individual areas to get total square footage. Make your next paint job easier.