Methodology
Formula & assumptions
Door-front area
door count × door width × door height
Use representative dimensions only within a truly similar door group.
Drawer-front area
drawer count × drawer width × drawer height
Split large and small drawer groups when dimensions vary significantly.
Purchase target
combined front area × (1 + entered allowance)
Keep cut/finish reserve separate from measured face area.
Packages to buy
round target ÷ package coverage up
Use the actual usable coverage for the selected finish product.