Net area for paint and drywall — subtract doors and windows from the gross wall
The calculator has add sections (rooms, walls, lots) and subtract sections (doors, windows, cutouts). For wall paint and drywall you want the net: a 14 × 8 wall (112 ft²) minus a door (21 ft²) and a window (12 ft²) = 79 ft². For flooring, usually keep the gross.
What this diagram shows
A wall elevation showing how to get net area by subtracting openings. The gross wall is 14 feet wide by 8 feet tall, or 112 square feet. A 3-by-7-foot door is subtracted at 21 square feet and a 4-by-3-foot window is subtracted at 12 square feet, both drawn as red cutouts. The equation reads 112 minus 21 minus 12, leaving a net of 79 square feet. The calculator adds sections for rooms, walls, and lots and subtracts sections for doors, windows, closets, and cutouts. For flooring you usually keep the gross area because you tile under the door swing, not the wall.
Square Footage Calculator
Free square footage calculator: add multiple rooms or odd shapes, subtract doors and windows, and convert to sq ft, sq yards, square meters and squares.
Related diagrams
Measuring & EstimatingWhat a board foot is — the ÷12 lumber formula and 144-cubic-inch definition
Measuring & EstimatingBoard feet uses nominal softwood and rough hardwood size, not the finished size
Measuring & EstimatingBoard foot vs linear foot vs square foot — three 8-foot boards compared
Measuring & EstimatingWhy a cubic yard is 27 cubic feet, not 3 — the volume formula in feet and inches
Measuring & EstimatingVolume take-off — footprint area × its own depth, adding pours and subtracting voids
Measuring & EstimatingCubic yards to an order — 45 bags a yard, or ready-mix concrete past about 1 cubic yard