Wall Square Footage Calculator

Wall square footage is the starting point for almost every interior and exterior project. Drywall, paint, siding, wallpaper, paneling, tile backsplash: they all get ordered off the same number. The math is easy once you know the trick, which is that you measure width times height and then take out the openings. Enter your dimensions below and the calculator does it for one wall or a full room.

How to calculate the square footage of a wall

A single wall is a rectangle, so its area is width times height.

A wall 14 feet wide and 8 feet tall is 14 x 8 = 112 square feet.
A wall 20 feet wide and 9 feet tall is 20 x 9 = 180 square feet.

That's the gross area. For most jobs you then subtract the openings: doors, windows, a fireplace, a large pass-through. A standard interior door is about 21 square feet and a common window around 15, though you should measure anything large. Take the gross wall area, remove the openings, and you've got the net square footage you'll actually cover.

Subtracting doors and windows correctly

The right way to subtract an opening is to measure its actual width and height, multiply for the area, and take that off the gross wall. Rules of thumb are fine for quick estimates, but real openings vary:

Opening	Typical size	Area to subtract
Standard interior door	3 ft x 6 ft 8 in	about 20 to 21 sq ft
Exterior entry door	3 ft x 6 ft 8 in	about 21 sq ft
Double or patio slider	6 ft x 6 ft 8 in	about 40 sq ft
Standard single window	3 ft x 4 ft	about 12 sq ft
Large picture window	6 ft x 4 ft	about 24 sq ft
Garage door (single)	9 ft x 7 ft	about 63 sq ft

The one trap is subtracting openings for the wrong job. For paint, siding, wallpaper, and paneling you genuinely skip those surfaces, so subtract them. For drywall you usually don't, which is covered below. When a wall is mostly glass or has a garage door in it, always subtract, because that's a big chunk of area you're not covering.

Doing all four walls of a room

For a whole room, add up the length of every wall (the perimeter) and multiply by the ceiling height. A rectangular room makes this a one-line calculation:

Perimeter x height = total wall area

Take a 12 by 14 room with 8 foot ceilings. The perimeter is 2 x (12 + 14) = 52 feet, and 52 x 8 = 416 square feet of wall before you remove any openings. Odd-shaped rooms work the same way once you measure each wall segment and add them up, which is the same break-it-into-pieces approach covered in the pillar guide on calculating square footage.

Now the number means different things depending on what you're buying.

Use case 1: drywall

Drywall comes in sheets, so you convert square footage into a sheet count.

A 4 by 8 sheet is 32 square feet.
A 4 by 12 sheet is 48 square feet.

Divide your total wall area (plus the ceiling, if you're hanging that too) by the sheet size, then add about 10 percent for waste and cuts. Longer 4 by 12 sheets mean fewer seams to tape, which is why pros favor them on big walls even though they're heavier to handle.

Here's how the two sheet sizes compare for common room totals, with the 10 percent waste factor already built in:

Wall + ceiling area	4 x 8 sheets (32 sq ft)	4 x 12 sheets (48 sq ft)
400 sq ft	14 sheets	10 sheets
584 sq ft (12 x 14 room)	21 sheets	14 sheets
800 sq ft	28 sheets	19 sheets
1,000 sq ft	35 sheets	23 sheets

Worked example. For the 12 by 14 room above, the walls are 416 square feet and the ceiling adds 12 x 14 = 168, for 584 square feet total.

Using 4 by 8 sheets: 584 / 32 = 18.25, round to 19, add 10 percent, so order about 21 sheets.
Using 4 by 12 sheets: 584 / 48 = 12.2, round to 13, add 10 percent, so order about 14 sheets.

Most drywallers don't bother subtracting small openings, because you hang the board right over a window rough opening and cut it out afterward, which keeps the seams clean. The offcuts also aren't always reusable. That waste is exactly why the 10 percent cushion exists. It's a running theme in trade forums: in a long thread on the Mike Holt forums about bad drywall installs, the recurring complaint is short-ordering and sloppy seams, not buying a few sheets too many.

The finishing materials scale with area too. A rough guide: about one 4.5 gallon box of joint compound and one roll of tape per 12 to 16 sheets, plus roughly a pound of screws per 1,000 square feet of board.

Use case 2: siding

Siding is ordered by the "square," where one square equals 100 square feet of coverage. So you take your exterior wall area, subtract the big openings, and divide by 100.

A wall section totaling 365 net square feet is 3.65 squares. Add waste and round up. Siding waste runs higher than drywall because of angle cuts around windows, doors, gables, and corners. Ten percent is a floor; a cut-up wall with lots of openings and a gable end can run 15 percent or more. Order to the square and keep a little extra, since dye-lot color can shift between orders the same way paint batches do.

Worked example. Say the front of a house is 30 feet wide and 10 feet tall at the walls, with two windows (15 square feet each) and a door (21). The rectangular wall is 30 x 10 = 300 square feet, minus 51 for the openings, so 249 net. That's 2.49 squares. Add 15 percent for a cut-up front with a door and windows, and you're at about 2.86 squares, so order 3 squares.

Measuring gable and triangular wall ends

A gable end is the triangle of wall between the top of the rectangular wall and the roof peak. Its area is base times height divided by 2. Measure the width of the wall at the eave line for the base, and the vertical height from that eave line straight up to the peak for the height.

Say the gable is 30 feet wide at the base and rises 8 feet to the peak. Area is 30 x 8 / 2 = 120 square feet, which is 1.2 squares. You add that triangle to the rectangular wall beneath it. Gable siding usually needs a heavier waste factor, 15 percent or more, because every course meets the roof line at an angle and each piece gets cut twice. If a wall has two gable ends (front and back), measure and add both. The same triangle formula covers any other angled wall end, like the slope under a shed roof or a staircase wall inside the house.

Use case 3: paneling and wainscoting

Paneling and wainscoting sell as sheets or as a coverage figure, so the wall square footage drives the count the same way drywall does.

Sheet paneling and beadboard come in 4 by 8 panels, 32 square feet each, the same as a drywall sheet. Divide net wall area by 32 and add 10 percent for cuts. Unlike drywall, subtract the openings here, because you cut paneling to fit around them and the offcuts rarely reuse. A full-height accent wall 14 feet wide and 8 feet tall is 112 square feet, or 4 panels once you round up and add waste.

Wainscoting runs only partway up, so measure the wall width times the wainscot height, not the full ceiling height. A 14 foot wall of 3 foot wainscoting is 14 x 3 = 42 square feet. Board-and-batten and picture-frame styles are figured the same way by the area they cover, then you buy the boards to suit.

Use case 4: paint

For paint, the wall square footage feeds straight into a coverage calculation. A gallon of interior latex covers roughly 350 to 400 square feet per coat, and most jobs need two coats. Rather than repeat all of that here, the paint square footage calculator walks through gallons, coats, primer, and dark-to-light color changes with its own worked example.

Common mistakes

Using floor area instead of wall area. A 12 by 14 room has 168 square feet of floor and 416 square feet of wall. For anything vertical, measure the walls.

Forgetting the ceiling. Drywall and paint jobs usually include the ceiling. That's floor area (length times width) added to your wall total.

Skipping the waste factor. Ten percent is standard for drywall, and siding often needs more. Ordering the exact math figure leaves you one cut short at the worst moment.

Subtracting tiny openings on drywall. You hang over small windows and cut them out, so subtracting them under-orders your sheets. Save opening subtractions for paint and siding, where you genuinely skip that surface.

Mixing up squares and square feet for siding. A square is 100 square feet. A 1,500 square foot exterior is 15 squares, not 1,500.

For roof surfaces, which also sell by the square and add pitch into the math, see the roof square footage calculator. To size the room first, start from the homepage.

Frequently asked questions

How do I calculate the square footage of a wall?

Multiply the wall's width by its height. A wall 14 feet wide and 8 feet tall is 112 square feet. For a job like paint or siding, subtract about 21 square feet per door and 15 per window to get the net area you'll actually cover.

How do I calculate square feet for a whole room's walls?

Add the length of all the walls to get the perimeter, then multiply by the ceiling height. A 12 by 14 room with 8 foot walls has a 52 foot perimeter, so 52 x 8 = 416 square feet of wall before openings. Add the ceiling area if you're drywalling or painting it.

How many drywall sheets do I need?

Divide total wall and ceiling area by the sheet size, then add about 10 percent for waste. A 4 by 8 sheet is 32 square feet and a 4 by 12 is 48. For 584 square feet, that's roughly 21 sheets of 4 by 8 or 14 sheets of 4 by 12 with waste included.

How do I calculate siding square footage?

Find the exterior wall area, subtract large openings, and divide by 100 to get the number of squares, since siding is sold by the square. Add 10 percent or more for waste, because angle cuts around windows and gables create a lot of scrap. Gable ends are triangles: base times height divided by 2.

Should I subtract doors and windows from wall square footage?

For paint and siding, yes, because you don't cover those surfaces. For drywall, most installers don't subtract small openings since the board is hung over them and cut out later. Always subtract very large openings like a garage door or a wall of glass.

How do I measure a gable or triangular wall?

Use base times height divided by 2. Measure the wall width at the eave line for the base and the vertical rise from the eave line to the peak for the height. A gable 30 feet wide and 8 feet tall is 30 x 8 / 2 = 120 square feet. Add that triangle on top of the rectangular wall below it.

How much drywall do I need for a 12x12 room?

A 12 by 12 room with 8 foot ceilings has 384 square feet of wall plus 144 for the ceiling, so 528 square feet total. Using 4 by 8 sheets at 32 square feet each, that's about 19 sheets with a 10 percent waste factor. Using 4 by 12 sheets, it's about 13.

How many 4x8 sheets of paneling do I need?

Divide the net wall area you're covering by 32 square feet per sheet, then add 10 percent for cuts. A 14 foot wide, 8 foot tall accent wall is 112 square feet, which rounds up to 4 panels with waste. Subtract door and window openings for paneling, since you cut around them and the scrap rarely reuses.

What waste factor should I use for siding?

Ten percent is the floor for a plain wall. Bump it to 15 percent or more for walls with lots of windows, doors, corners, or a gable end, since every angle cut creates scrap. Order to the nearest full square and keep a little extra, because color can shift slightly between production lots.

Wall Square Footage Calculator