How to measure
Use these guides to identify the measurements the calculator needs. Drawings are not to scale.
C · Wall height: measure vertically from floor to ceiling. Four walls have area 2 × (length + width) × height; the ceiling is length × width.
For openings, multiply each opening’s width by its height and add the areas. Exclude only openings in the surfaces selected. For irregular rooms, calculate separate rectangles or enter a known total surface area.
A room-sized estimate
A 12 × 10 ft room with 8 ft walls has 352 sq ft of wall surface. With two coats, 10% extra, and coverage of 350 sq ft per US gallon, it needs about 2.21 US gallons. Three whole gallons is a buying reference; choose the actual container combination your store sells.
How it works
Wall area is 2 × (length + width) × height. Ceiling area is length × width. Select the surfaces you need, subtract any openings, add extra, multiply by coats, and divide by coverage. Known area skips the room calculation. A US gallon is 3.785411784 liters.
The Sherwin-Williams paint calculator gives a typical range of 350–400 sq ft per gallon. The default uses the lower end, and you can change it. Follow your product label for rough surfaces, porous walls, and major color changes. Extra is a planning allowance, not a guarantee.
Calculate each color and product separately. Ceiling paint, wall paint, primer, and trim often have different requirements. The tool does not calculate labor, cost, drying time, or preparation.
Putting up new walls first? The drywall calculator estimates sheets, compound, tape, and screws. For floor area and flooring quantities, use square footage.