Paint calculator: how much paint do I need for a room?

How much paint do I need? The math in words

1. Add the four walls: twice the length plus twice the width. That is the room's perimeter.
2. Multiply the perimeter by the wall height. That is the wall area.
3. Take off the doors and windows: 21 square feet for each door and 15 for each window, the allowances in Sherwin-Williams' training for painters.^[1]
4. Multiply by the number of coats. Two is the usual answer: paint makers call for two coats for an even finish, and Benjamin Moore lists one or two for its Regal Select.^[2][3]
5. Divide by what one gallon covers. Sherwin-Williams' training divides by 350 square feet a gallon for one coat on a smooth wall.^[1] Round up to whole gallons.

Example: a 12 by 14 foot bedroom with 8 foot walls, one door and two windows. Perimeter: 2 × (12 + 14) = 52 feet. Wall area: 52 × 8 = 416 square feet. Openings: 21 + 2 × 15 = 51 square feet, so 365 square feet to paint. Two coats: 730 square feet ÷ 350 = 2.09 gallons. Buy 3 gallons, or 2 gallons and a quart.

Square footage of walls for paint: doors, windows and the ceiling

The wall area counts every wall from floor to ceiling, so the openings come off before you divide. Sherwin-Williams' worked room is 16 by 12 feet with 8 foot walls: 448 square feet of wall, less two doors at 21 and three windows at 15, leaves 361 square feet, which is 1.03 gallons for one coat.^[1] Type the door and window counts in the calculator; change the size of each when yours are bigger.

• A wide opening, a patio door or a double door: multiply its width by its height in feet and type that as one door, or count it as two doors.
• The ceiling: tick Include the ceiling and the calculator adds length times width. Ceiling paint is often a different can, so many painters work it out on its own.
• Closets: their walls are part of the job. Add the closet as its own room, or add its wall lengths to the perimeter.

Coats and coverage: what one gallon covers

Sherwin-Williams says a gallon of paint typically covers about 350 to 400 square feet, a quart about 100, and a gallon of primer only 200 to 300.^[4] A premium paint can stretch further: Benjamin Moore lists 400 to 450 square feet a gallon for Regal Select.^[3] The calculator starts at 350, the low end, so a textured wall or a porous one does not leave you short. Type the number from your can's label to use your paint's own coverage.

New drywall, a patched wall or a big color change takes primer first. Run the calculator again with one coat and the primer's coverage from its label.

Paint for a whole house from a floor plan

Work room by room: each room's perimeter times its wall height, less its own doors and windows. A wall between two rooms gets painted on both sides, and the room-by-room math counts it twice, which is right for paint. Then add the rooms, multiply by the coats and divide by the coverage once. For the floor area of the same rooms, the square footage calculator adds rectangles the same way.

A plan's whole-house wall area is a different number. On a PlaceAnew report it counts each wall once, before doors and windows come out, so use it as a cross-check and order paint from the rooms. How to estimate materials from a floor plan works through paint, drywall and flooring from one real scan.

Every wall in the house from one walk

Painting quotes eat time in the measuring: a tape, a ladder for the height, and every door and window counted room by room. PlaceAnew does it in one walk. Hold an iPhone or iPad with LiDAR (iPhone 12 Pro or a newer Pro model, or an iPad Pro from 2020 or later), walk through the rooms, and the floor plan comes out with every room's size and area, every door and window, and the walls in 3D. The PDF report adds a property summary with the wall area, the average ceiling height and the door and window counts. Scanning, floor plans, 3D, editing, the kitchen designer with prices and exports are free.

The sizes hold up. In one walk of our own office, all seven wall lengths that compare one to one came within 2.5 inches of the hand-measured plan.^[5] Type the room sizes from the plan into this calculator, or send the PDF with the quote so the client sees exactly which walls are priced.

Questions people ask