Drywall Calculator

How to use the drywall calculator

This drywall calculator answers the question every hanging job starts with: how many sheets of drywall do I need? It works out the area you will cover, takes off the doors and windows, adds a waste allowance, divides by the size of one sheet and rounds up. It also lays out every wall in whole sheets, so you can see what a different sheet size or direction would save, and it lists the joint compound, tape, screws and corner bead that go with the sheets. All of the math happens in your browser.

1. Choose what you are measuring. Under Measure, pick Whole room (length, width and wall height, with the ceiling if you like), Wall by wall (any number of separate walls), Ceiling only, or Known area if you already have the square footage.
2. Count the doors and windows. Enter how many there are and their size once, under Doors, windows and other openings. Add anything else at its exact size, such as a patio door, a pass-through or a skylight. Every length field has its own unit, and you can type 8' 6", 96 in or 2400 mm.
3. Pick the sheets. Choose a sheet size, or a custom size, and whether the wall sheets are hung horizontally or vertically. The waste starts at 10%, our own starting value; change it to suit the job. Choose whether the shopping list counts sheets by area plus waste or by the layout of each wall.
4. Check the rates. The framing and screw spacing, the joint compound per 100 sq ft, the compound container, the tape roll and the corner bead stick all have editable starting values. Add prices if you want a cost.
5. Read what to buy. The results show the sheets to buy, both counts side by side, a shopping list, the cost and a table of every surface with its area, its sheets by layout and the length of its joints. Copy the results, download them as a CSV file or print them.

Switch Units to Metric to see square meters, meters and liters. The calculator remembers your last entries on this device.

How to measure a room for drywall

A tape measure and a notepad are all you need. Measure in whatever units you like; the calculator converts them.

• Wall widths. Measure each wall along the floor, corner to corner. For a rectangular room the length and the width are enough, because opposite walls match. For an L-shaped room, a basement with a few walls to frame, or a room with a sloped ceiling, use Wall by wall, or work out the floor plan with the square footage calculator first.
• Wall height. Measure from the floor to the ceiling framing. The height decides how many rows of sheets each wall takes, so it matters for the layout as much as for the area.
• Doors and windows. Measure the rough openings. Big openings save whole sheets; small ones are often covered and cut out, which is why the layout count ignores them.
• Framing. Check the stud and joist spacing, usually 16 or 24 inches on center. It sets how many screws each sheet takes.
• Corners. Count the inside corners, which are taped, and the outside corners, which take corner bead.

How to calculate how many sheets of drywall you need

The common method takes five steps. The calculator does them for the walls and for the ceiling:

wall area     = perimeter × wall height
area to cover = wall area − doors − windows − other openings (+ ceiling)
sheets        = area to cover × (1 + waste ÷ 100) ÷ sheet area, rounded up

1. Measure the walls. Multiply each wall's width by its height and add them up, or multiply the room's perimeter by the wall height.
2. Take off the openings. Subtract the width times the height of each door, window and other opening.
3. Add the ceiling. If you are covering the ceiling too, add its length times its width.
4. Add the waste. Multiply the area by one plus the waste percentage, so by 1.10 for 10% waste.
5. Divide by the sheet area. Divide by the area of one sheet, 32 sq ft for a 4 × 8 sheet, and round up to whole sheets.

Example: a 12 × 12 ft room with 8 ft walls, one 36 × 80 in door and two 36 × 48 in windows. The perimeter is 48 ft, so the walls are 48 × 8 = 384 sq ft. The door is 20 sq ft and each window 12 sq ft, 44 sq ft in all, which leaves 340 sq ft to cover. With 10% waste that is 340 × 1.10 ÷ 32 = 11.69 sheets, so you buy 12 sheets of 4 × 8 drywall. Laid out wall by wall, each 12 ft wall takes two rows of one and a half sheets, three sheets a wall, and the layout count agrees: 12 sheets. That is the example the calculator opens with.

The two counts rarely match exactly. The area count spreads the waste evenly over the job; the layout count follows the actual walls, so short walls, odd heights and lengths that don't divide into whole sheets show up in it. When they disagree, the larger number is the safer one to buy, and the layout tells you which walls cause the difference.

Drywall sheet sizes

Drywall, also called gypsum board or wallboard, comes in sheets 4 ft wide in the United States, and 1200 mm wide in many metric markets. The lengths below are the ones the calculator lists. They are common sizes rather than a standard list, so check what your supplier sells; the Custom size option takes any sheet from 6 in to 20 ft a side.

Longer sheets mean fewer joints to tape, but they are heavier and harder to carry up stairs and through doors. A sheet that is as long as the wall, such as a 12 ft sheet on a 12 ft wall, leaves no butt joint in the row at all. For the example room, 4 × 12 sheets cut the count to 8 and the tape to 80 ft, against 112 ft with 4 × 8 sheets.

Hanging drywall horizontally or vertically

The building code lets you choose. Section R702.3.5 of the 2024 International Residential Code says: "Gypsum board and gypsum panel products shall be applied at right angles or parallel to framing members. All edges and ends of gypsum board and gypsum panel products shall occur on the framing members, except those edges and ends that are perpendicular to the framing members." Hung horizontally, a sheet's long edge runs across the studs; hung vertically, it runs along them.

The direction changes the layout. The calculator lays every wall out in rows: a wall takes as many rows as its height needs, each row is a full row of sheets, and the piece cut off the end of one row starts the next row on the same wall. With 8 ft walls, two horizontal rows of 4 ft sheets fit exactly. With 9 ft walls they don't, and a third, narrow row is needed:

• 4 × 8 sheets, horizontal: three rows a wall, 20 sheets for a 12 × 12 ft room with 9 ft walls.
• 4 × 9 sheets, vertical: one row of three sheets a wall, 12 sheets for the same room.
• 4 × 12 sheets, horizontal: three rows of one sheet a wall, 12 sheets, with the narrow top row cut from full sheets.

By area, the same room needs 14 sheets of 4 × 8 with 10% waste, because the area count assumes the narrow strips can be cut from offcuts. The layout count is the cautious one: it keeps every cut piece on the wall it came from. Choose By layout of each wall under Count to buy to make the shopping list follow it.

How much waste to add

Every job loses some board to cut-outs, end cuts, mistakes and damaged corners. We found no government, extension or standards-body figure for an ordering allowance, so the calculator's 10% is our own starting value, not a cited number. Raise it for rooms with many short walls, angles, soffits or cut-outs, and lower it for big plain walls where the layout count already shows little loss.

• No waste: 10.63 sheets, so 11 to buy for the example room.
• 10% waste: 11.69 sheets, so 12.
• 15% waste: 12.22 sheets, so 13.

A spare sheet is also handy for patches later, and leftover board keeps well flat and dry.

Doors, windows and other openings

The area count takes each door and window off at the size you enter, starting at 36 × 80 in for a door, which is 20 sq ft, and 36 × 48 in for a window, which is 12 sq ft. Anything else goes under Other openings at its exact size: a patio door, a wide pass-through, a fireplace or built-in shelves. In Ceiling only mode, other openings come off the ceiling instead, which is where skylights and attic hatches go.

For example, a 6 ft × 80 in patio door in the example room takes another 40 sq ft off, leaving 300 sq ft and 11 sheets by area. The layout count stays at 12, because sheets are usually hung across an opening and the opening is cut out afterward, so the piece that comes out is rarely big enough to use elsewhere.

Drywall for a ceiling

A ceiling is its length times its width. In Whole room mode, tick Also cover the ceiling. The calculator counts the ceiling separately, because ceilings are often hung with a different board: the 12 × 12 ft example ceiling is 144 sq ft, which takes 5 sheets of 4 × 8 with 10% waste, for 17 sheets in all. The ceiling also adds the angle where the walls meet it to the tape, and it takes more screws, because the code's screw spacing on ceilings is closer.

For a ceiling on its own, choose Ceiling only. A 12 × 10 ft ceiling is 120 sq ft: 4.13 sheets by area, so 5 to buy, and the layout agrees at 5. The layout runs each sheet's length along the ceiling's longer side, across the joists.

Ceiling board is heavy and is held overhead while it is fastened, so plan for a helper or a drywall lift, and follow the code's spacing for the framing and the screws in the next sections.

How much drywall tape you need

Tape covers every joint between sheets, every inside corner and, with a new ceiling, the angle where the walls meet it. The calculator measures all three from the layout, rather than guessing a length per sheet:

• Joints. The seams between rows plus the butt joints in each row, for every wall and the ceiling.
• Inside corners. Four for a whole room, or the number you enter in Wall by wall mode, each the height of the wall.
• The ceiling angle. The room's perimeter when you cover the ceiling.

In the example room each wall has one row seam 12 ft long and one butt joint in each row, 20 ft a wall and 80 ft in all, plus 32 ft of inside corners: 112 ft of tape, or 1 roll of 250 ft. With the ceiling, its joints and the 48 ft ceiling angle bring it to 196 ft.

In Known area mode there is no layout, so the tape is estimated at one sheet length plus one sheet width of joint per sheet of area, the share of each sheet's edges in a large wall. For 1,000 sq ft of 4 × 8 board that is about 375 ft. Roll lengths of 250 ft are common, but check what your store sells.

How many drywall screws per sheet

The International Residential Code sets the most the fasteners may be spaced. In Table R702.3.5 of the 2024 edition, for board hung without adhesive, the maximum screw spacing is 16 in on walls with framing 16 in on center, 12 in on walls with framing 24 in on center, and 12 in on ceilings. Section R702.3.5.1 adds: "Screws for attaching gypsum board and gypsum panel products to wood framing shall be Type W or Type S in accordance with ASTM C1002 and shall penetrate the wood not less than 5/8 inch (15.9 mm)." The same section and table numbers appear in the 2021 edition. Your local code may differ, so check with your building department.

The calculator counts the framing members a sheet crosses and the screws along each one, both ends included:

members  = side across the framing ÷ framing spacing, rounded down, + 1
per line = side along the framing ÷ screw spacing, rounded up, + 1
screws   = members × per line

A 4 × 8 sheet hung horizontally on studs 16 in on center crosses 7 studs with 4 screws on each, 28 screws. On a ceiling at 12 in spacing it takes 7 × 5 = 35. The example room with its ceiling needs 511 screws. With framing 24 in on center and screws at 12 in, a wall sheet takes 25. Screws are sold by the box or by weight, so buy a little over the count.

Joint compound and corner bead

Joint compound, often called mud, covers the tape, the screw heads and the corner bead, usually in a tape coat and two finish coats. How far it goes depends on the product, the finish you want and how smooth the joints are, and we found no government or standards-body figure for it. The calculator starts at 1 gallon per 100 sq ft of board, which is about 0.41 L per m², as a rough starting value; replace it with the coverage on your compound's label.

The example room's 340 sq ft of walls take 3.40 gallons, which is 1 container of 4.5 gallons. With the ceiling it is 4.84 gallons, so 2 containers. Pail sizes vary, so set the container to the one your store sells.

Corner bead protects outside corners, the edges that stick out into a room. Enter how many outside corners there are, and the calculator gives each one a piece the height of the wall: two outside corners on 8 ft walls are 16 ft, or 2 sticks of 8 ft. Add window returns, soffits and arches under Other corner bead.

Drywall thickness and the building code

Thickness does not change the counts, so the calculator shows it as information only, with what the 2024 International Residential Code says about each choice. Table R702.3.5 lists the maximum framing spacing for 3/8, 1/2 and 5/8 inch board:

• 3/8 in: walls with framing up to 16 in on center, and ceilings up to 16 in when hung perpendicular to the framing. The table's footnote adds: "Three-eighths-inch-thick single-ply gypsum board or gypsum panel product shall not be used on a ceiling where a water-based textured finish is to be applied, or where it will be required to support insulation above a ceiling."
• 1/2 in: walls with framing up to 24 in on center; ceilings up to 16 in in either direction, or 24 in when hung perpendicular.
• 5/8 in: walls and ceilings with framing up to 24 in on center, with ceilings at 24 in hung perpendicular.

Garages. Table R302.6, in the code's chapter on building planning, calls for "Not less than 1/2-inch gypsum board or equivalent applied to the garage side" between the garage and the house and its attic, and "Not less than 5/8-inch Type X gypsum board or equivalent" under rooms above the garage. Wet areas. Section R702.3.7.1 says: "Water-resistant gypsum backing board shall not be used where there will be direct exposure to water, or in areas subject to continuous high humidity." Tile in showers and around tubs goes on a backer board instead; the tile calculator covers the tile.

Local codes adopt and amend these rules, so check with your building department before you start, especially for garages, fire-rated walls and anything structural.

Metric: square meters and 1200 mm sheets

Switch Units to Metric to see areas in square meters, tape and corner bead in meters and joint compound in liters. Pick a 1200 mm sheet, or type your own size, and enter the framing in millimeters if that is how it was built.

Example: a room 4 × 3.5 m with walls 2.5 m high has 37.5 m² of wall. A 0.9 × 2 m door and a 1.2 × 1.2 m window leave 34.26 m². With 10% waste and 1200 × 2400 mm sheets of 2.88 m², that is 13.09 sheets, so 14 to buy. The walls are 2.5 m high, just over two horizontal rows, so the layout count is 20. Hung vertically, 1200 × 2700 mm sheets cover the height in one piece and the layout drops to 14.

The conversions are exact: an inch is exactly 2.54 centimeters and a foot exactly 0.3048 meters, as the National Institute of Standards and Technology (NIST) lists in Handbook 44, Appendix C and Special Publication 811. So a square foot is exactly 0.09290304 square meters, and a US gallon of compound is exactly 231 cubic inches, 3.785411784 liters.

Sanding dust

Sanding joint compound makes a fine dust that spreads through a house. The National Institute for Occupational Safety and Health (NIOSH) warns, in Control of Drywall Sanding Dust Exposures: "Over time, breathing the dust from drywall joint compounds may cause persistent throat and airway irritation, coughing, phlegm production, and breathing difficulties similar to asthma." It adds: "When silica is present, workers may also face an increased risk of silicosis and lung cancer."

Smooth each coat well before it dries so there is less to sand, close off the room, and follow the safety directions on the compound's label and data sheet. The NIOSH document describes sanders with dust collection that reduced the dust workers breathed.

Old walls: asbestos and lead

New drywall often goes up after old walls or ceilings come down, and that is where the risk is. The U.S. Environmental Protection Agency lists, among the places asbestos may be found, "Textured paint and patching compounds used on walls and ceilings", and its advice for anything you are unsure of is plain: "If in doubt, treat the material as if it contains asbestos and leave it alone." EPA recommends a trained and accredited asbestos professional for sampling and removal; read Learn About Asbestos and Protect Your Family from Exposures to Asbestos before you tear anything out.

Old paint is the other concern. EPA notes: "If your home was built before 1978, it is more likely to have lead-based paint." Its page Protect Your Family from Sources of Lead explains how to work safely around it.

How we calculate

Every figure in the tool and on this page comes from the same code, and the examples above are checked against it automatically.

• Lengths. Every measurement is converted to feet first: inches ÷ 12, centimeters ÷ 30.48, millimeters ÷ 304.8, meters ÷ 0.3048, the exact NIST definitions.
• Area. Walls = width × height for each wall; in a whole room, the four walls are length, width, length, width at one height. Ceiling = length × width. Doors, windows and other openings come off the walls, or off the ceiling when there are no walls.
• Sheets by area. Area × (1 + waste ÷ 100) ÷ sheet area, rounded up, separately for the walls and the ceiling.
• Sheets by layout. For each wall, rows = height ÷ the sheet side that runs up the wall, rounded up; sheets = rows × width ÷ the side that runs along it, rounded up. Cut pieces are reused on the same wall only, and openings are ignored. Ceilings run the sheet length along the longer side.
• Tape. Joints from the layout + inside corners × wall height + the ceiling angle; in Known area mode, area × (sheet length + sheet width) ÷ sheet area.
• Screws. (Side across the framing ÷ framing spacing, rounded down, + 1) × (side along the framing ÷ screw spacing, rounded up, + 1) per sheet, wall sheets and ceiling sheets apart.
• Compound and bead. Area ÷ 100 × the compound rate; outside corners × wall height + other runs for corner bead, one piece per corner where it fits.
• Cost. What you buy × your prices. Nothing is filled in for you, because prices vary from store to store.

The calculator does not count furring, insulation, adhesive, primer, paint or labor, and it does not reuse offcuts from one wall on another. The waste and compound rates are starting values: set them from your own job and the labels of what you buy.

Your measurements stay on your device

The calculator runs entirely as JavaScript in your browser tab. Nothing you enter is uploaded: the page's Content-Security-Policy allows connections only back to this site, and the tool has no code that sends anything anywhere. It remembers your last measurements and settings in your browser's local storage, on your device only. There is no account and no cookie.

Sources

• International Code Council: 2024 International Residential Code, Chapter 7, Wall Covering: Section R702.3.5 and Table R702.3.5 (application, framing and fastener spacing), R702.3.5.1 (screws) and R702.3.7.1 (water-resistant backing board).
• International Code Council: 2024 International Residential Code, Chapter 3, Building Planning: Section R302.6 and Table R302.6, dwelling unit garage separation.
• National Institute for Occupational Safety and Health: Control of Drywall Sanding Dust Exposures, DHHS (NIOSH) Publication No. 99-113.
• U.S. Environmental Protection Agency: Learn About Asbestos, on where asbestos may be found.
• U.S. Environmental Protection Agency: Protect Your Family from Exposures to Asbestos.
• U.S. Environmental Protection Agency: Protect Your Family from Sources of Lead, on lead-based paint in homes built before 1978.
• National Institute of Standards and Technology: NIST Handbook 44 (2026), Appendix C, General Tables of Units of Measurement: 1 foot = 0.3048 meter, 1 inch = 2.54 centimeters and 1 US gallon = 231 cubic inches, exactly.
• NIST Special Publication 811, Appendix B.9, Factors for units listed by kind of quantity: exact factors for the foot, the inch and the gallon.

Reviewed by microplugins · Last updated October 2026

This is an educational tool, not professional construction advice. Sheet sizes, waste, compound coverage and code rules vary: check what your supplier sells, the labels of what you buy and the building code where you live.