How to estimate paint for a room
Interior wall paint is driven by wall area rather than floor area. PrepMyBuild calculates the room perimeter, multiplies it by ceiling height, subtracts planning allowances for doors and windows, applies the number of coats, and divides by the coverage rate you select.
Coats can matter more than room size
Two coats approximately double the paint applied compared with one coat. Coverage can also change with surface texture, color change and product choice.
Doors and windows are planning deductions
The calculator uses standard opening allowances rather than asking you to measure every opening. For unusually large glass areas or doors, adjust your inputs or treat the result as a conservative planning estimate.
Primer is kept separate
Primer has its own toggle because it is not required for every repaint. New drywall, stains, repairs and large color changes are examples where primer may be considered.
After standard door/window deductions, the calculator estimates the net wall area and converts two coats into a paint quantity using the selected coverage rate.