Audited 27 Jul 2026·Last updated 28 Oct 2026·5 citations·Tier 1·0 uses

Drywall Calculator

Work out how many 4×8, 4×12 or other drywall sheets a room needs from wall perimeter, height, ceiling, openings and waste, plus screws and board cost.

Drywall Calculator

Sheet count (whole sheets)
20
Whole sheets of the size you entered needed to cover the waste-adjusted area, always rounded up to the next full sheet.
Gross drywall area
640
Net drywall area after openings
576
Waste-adjusted drywall area
633.6
Estimated screw count
640
Estimated material cost
310.00

Background.

A 12 by 16 foot bedroom with 8-foot walls has 448 square feet of wall and a 192-square-foot ceiling. Take out two doors and two windows and 576 square feet remain to be covered, which sounds like exactly 18 sheets of 4 × 8 drywall at 32 square feet apiece. The order that actually finishes the room is 20. Gypsum board is bought by the whole sheet, every outlet, door head and inside corner leaves offcuts that rarely fit anywhere else, and a sheet with a crushed corner is little use on a ceiling.

The estimate here follows the same steps a careful estimator takes on paper: wall perimeter times height, plus the ceiling if you are boarding it, minus the openings, plus a waste allowance, divided by the area of the sheet you plan to buy, and only then rounded up to a whole sheet. Sheet size changes the answer more than people expect. The same bedroom takes 14 sheets of 4 × 12, and each of those weighs half as much again as a 4 × 8 of the same board and needs a clear path from the truck to the room.

Two extras ride on the sheet count. Enter a price per sheet and you get the cost of the board itself; enter a screws-per-sheet figure and you get a fastener count to shop against. What the arithmetic cannot tell you is which way to hang the sheets, what thickness a ceiling needs, or whether a wall has to be fire-rated. Those choices come from the framing, the building code and the board maker's instructions, and the questions further down deal with the ones that change what you buy.

What is drywall calculator?

Drywall, also called gypsum board, plasterboard or by the trade name Sheetrock, is a panel with a core of gypsum (calcium sulfate dihydrate) faced on both sides with heavy paper. In the United States its dimensions and properties are specified by ASTM C1396. Most stock is 4 feet wide, with 54-inch board made so that two sheets laid horizontally cover a 9-foot wall, and full-size sheets start at 8 feet long, with 10 and 12 feet the other common lengths. The long edges are tapered slightly so tape and joint compound can fill the seam flush; cut ends are square, which is why end-to-end butt joints are harder to hide. Half-inch board is the ordinary wall thickness, five-eighths is common on ceilings and in fire-rated work, and quarter-inch is used to bend around curves or overlay an old surface. A drywall estimate turns the surfaces you intend to cover into a count of whole panels of one chosen size, with an allowance for the board lost to cutting.

How to use this calculator.

  1. Wall perimeter: add the lengths of every wall you are boarding, in feet. For a plain rectangular room that is twice the length plus twice the width, so a 12 × 16 room gives 56. Include closet walls and leave out any wall that is staying as it is.
  2. Wall height: floor to ceiling, in feet. If one part of the room is taller, or has a gable or a slope, enter the common height here and add the extra area to the ceiling figure, as described in the questions below.
  3. Ceiling area: the ceiling's length times width if you are boarding it, or 0 for walls only. If the ceiling will get a different board from the walls, leave it out and estimate it as a second run.
  4. Opening area: the total of doors, windows and pass-throughs that get no board. A 36 × 80-inch door is 20 sq ft and a 3 × 4-ft window is 12 sq ft; outlet boxes and vents are too small to bother deducting.
  5. Sheet length, sheet width and waste allowance: enter the board you intend to buy, such as 8 × 4, 12 × 4, or 12 × 4.5 for 54-inch board, and a waste percentage. Ten percent suits a plain room; go higher for many corners, soffits, angled walls or a first job.
  6. Price per sheet and screws per sheet are optional. Use the shelf price of the exact board you will buy, and scale the screw figure with the sheet: 32 for a 4 × 8 is one per square foot, so 48 for a 4 × 12.

The formula.

Sheets = ⌈ (A − O) × (1 + w) ⁄ S ⌉
A · wall area (perimeter × height) plus ceiling area, sq ftO · doors, windows and other openings, sq ftw · waste allowance as a fraction (10% = 0.10)S · area of one sheet, length × width, sq ft⌈ ⌉ · round up to the next whole sheet

Sheets = ⌈(A − O) × (1 + w) ÷ S⌉. A is the total surface: wall perimeter times wall height, plus the ceiling area. Multiplying perimeter by height assumes every wall runs the full height you entered, which is why gables, slopes and dropped soffits need adding separately. O is the opening area, and subtracting it gives the net area that will actually receive board. The waste fraction w (10% entered as 0.10) is applied to that net area, so the allowance covers surface you are boarding rather than the doors and windows you took out. S is the area of one sheet, length times width: 32 sq ft for a 4 × 8, 48 for a 4 × 12, 54 for 54-inch board 12 ft long. Dividing gives a fractional number of sheets, and the ceiling brackets round it up to the next whole sheet once, at the very end; 19.01 sheets becomes 20 exactly as 19.8 does. That last step makes the count lumpy. A small rise in area or waste can add a whole sheet, while a bigger change may add nothing because it is absorbed by the slack in the last sheet. The screw count is the whole-sheet count times your screws per sheet, and the board cost is the whole-sheet count times the price per sheet, because you pay for every sheet you carry home, including the part that ends up as offcuts. Layout sits outside the formula: it does not know where studs and joists fall, which way you will hang the board, or whether an offcut from one wall can finish another. The waste percentage is the single number that stands in for all of that.

A worked example.

Example

Take the 12 × 16 ft bedroom with 8-ft walls that the default values describe. The perimeter is 2 × 12 + 2 × 16 = 56 ft, so the walls come to 56 × 8 = 448 sq ft, and the 192 sq ft ceiling brings the gross area to 640 sq ft. Two 36 × 80-inch doors at 20 sq ft each and two 3 × 4-ft windows at 12 sq ft each make 64 sq ft of openings, leaving a net area of 576 sq ft. A 10% waste allowance raises that to 576 × 1.10 = 633.6 sq ft. Each 4 × 8 sheet covers 32 sq ft, and 633.6 ÷ 32 = 19.8, which rounds up to 20 sheets; nineteen would cover only 608 sq ft. At 32 screws per sheet that is 20 × 32 = 640 screws, and at $15.50 a sheet the board costs 20 × $15.50 = $310.00. The rounding has a consequence worth knowing if the ceiling is to get a different board. Estimated on their own, the walls need 384 × 1.10 = 422.4 sq ft, or 13.2 sheets, so 14; the ceiling needs 192 × 1.10 = 211.2 sq ft, or 6.6 sheets, so 7. Kept apart, the two products come to 21 sheets rather than 20, because each run rounds up separately.

opening Area Sq Ft64
sheet Length Ft8
screws Per Sheet32
perimeter Ft56
wall Height Ft8
waste Percent10
price Per Sheet15.5
ceiling Area Sq Ft192
sheet Width Ft4

Frequently asked questions.

Should drywall sheets run horizontally or vertically on the walls?
On residential walls up to about 8 feet, hangers usually run sheets horizontally. Each sheet then spans more studs, which bridges small irregularities in the framing, and the long seam lands at waist height where it is easy to tape. It often means fewer feet of joint, too: a 12-ft wall 8 ft high hung with two 4 × 12 sheets has one 12-ft seam, while 4 × 8 sheets stood on end leave two 8-ft seams, 16 ft in all. Orientation does not change the area, so it does not change the sheet count here, only the offcuts and the finishing work.
Do I deduct every window and door from the drywall area?
Deduct openings that are large and plainly get no board: doors, big windows, a wide pass-through. Be cautious with a small window in the middle of a wall, because the piece cut out of the sheet is rarely usable elsewhere, so deducting it shrinks the estimate without saving a sheet. Where a wall is broken up by several small openings, a slightly higher waste percentage is a better adjustment than a large deduction. Openings come off before the waste allowance is added, so the allowance only applies to surface that is boarded.
Are 4 × 12 sheets worth it compared with 4 × 8?
Longer sheets mean fewer butt joints, the seams hardest to make invisible, and fewer sheets to lift: the example bedroom needs 14 sheets of 4 × 12 against 20 of 4 × 8. The trade-off is handling. A 4 × 12 weighs half as much again as a 4 × 8 of the same board, takes two people, and may not turn the corner of a staircase or fit in the vehicle you have. Long board suits long walls in open spaces such as basements; 4 × 8 suits closets, small rooms and upstairs rooms reached by a tight stair. Compare prices per square foot rather than per sheet: $15.50 for a 4 × 8 is about 48 cents a square foot.
How much waste should I allow for drywall?
Ten percent is the usual starting point for a plain rectangular room, and 15 percent or more is reasonable for rooms with many corners, soffits, angled ceilings or small openings, or for a first-time hanger who will miscut a sheet or two. Because of the round-up, the allowance is sometimes free: in the example bedroom any waste figure up to about 11.1 percent still gives 20 sheets, while 12 percent tips the order to 21. Large unbroken walls hung with long sheets can get by with less.
Does the ceiling need a different board from the walls?
Often. Ceilings are normally boarded across the joists, and half-inch wall board can sag between framing spaced 24 inches apart, so ceilings are commonly done in five-eighths board or in half-inch sag-resistant ceiling board. When the products differ, estimate them separately. For a ceiling-only run, enter the ceiling area and set the wall perimeter and wall height to 0; with no ceiling area the walls must both be above zero. Remember that each run rounds up on its own.
What drywall goes on the wall between an attached garage and the house?
That wall, and a garage ceiling with rooms above it, are fire separations under residential building codes, which require gypsum board on the garage side and fire-rated Type X board on a ceiling below living space. Type X has glass fibres mixed into its core so it holds together longer in a fire. Estimate those surfaces as a separate run with the correct product, and check the thickness and fastening your local code and the board's listing require. A sheet count says nothing about whether a wall meets a fire rating.
Can I use regular drywall in a bathroom?
Moisture-resistant board is the usual choice for bathroom walls and ceilings away from the shower. Behind tile in a tub or shower surround, codes call for a tile backer such as cement board, fibre-cement board or a glass-mat gypsum backer rather than paper-faced drywall, because water working through grout would ruin the paper. Add the surround to your opening area so it drops out of the drywall count, then estimate the backer as its own run; cement board commonly comes in 3 × 5 ft sheets, so set the sheet size to match.
How many drywall screws do I need, and what kind?
The default of 32 per 4 × 8 sheet works out to one screw per square foot of board, a common rule of thumb for walls; ceilings are fastened more closely, so allow more for them, and scale the figure up for longer sheets. For half-inch board on wood studs, 1¼-inch coarse-thread drywall screws are the standard choice, while steel studs need fine-thread screws. Screws are usually sold by weight, so turn the count into boxes using the number per pound printed on the package.
Does the material cost include tape, joint compound and corner bead?
No. It is the whole-sheet count times your price per sheet and nothing else. Tape, compound, corner bead, screws, adhesive and primer are extra, and the compound bill depends heavily on the finish level, a scale running from Level 0 (board hung but untaped) to Level 5 (a skim coat over the entire surface). A Level 5 wall under raking light uses far more compound than a Level 2 garage wall, so estimate it separately from the net area shown here.
How do I measure a room with a sloped ceiling, a gable wall or a stairwell?
Wall area is perimeter times one height, so enter the height the walls share and add the odd shapes on top. A gable triangle is half its base times its rise: a 12-ft-wide gable rising 4 ft adds 24 sq ft. A sloped ceiling's area is its width times the length measured along the slope, not the floor dimension underneath. Because the ceiling figure is simply added to the wall area, you can put these extra square feet in the ceiling box, and the sheet count comes out right as long as every surface uses the same board.

References& sources.

  1. [1]ASTM International (2024). "ASTM C1396/C1396M: Standard Specification for Gypsum Board." ASTM.
  2. [2]Gypsum Association (2024). "Application and Finishing of Gypsum Panel Products, GA-216-2024." Gypsum Association Publications.
  3. [3]International Code Council (2024). "2024 International Residential Code, Chapter 7: Wall Covering." ICC.
  4. [4]National Institute of Standards and Technology (2026). "NIST Handbook 133, Appendix E: General Tables of Units of Measurement." U.S. Department of Commerce.
  5. [5]Bureau International des Poids et Mesures (2019). "The International System of Units (SI Brochure), 9th edition." BIPM.

How this page was produced

Published by
Quanta Calculator
Overseen by
Daniel, Quanta Calculator Researcher
Primary sources
5 cited below
Method
Sheets = ⌈ (A − O) × (1 + w) ⁄ S ⌉
Published
Last verified

Built with AI assistance and verified by automated tests against the cited sources — every worked example on this page is computed by the same code that runs the calculator. How we build and check calculators.

Related calculators
5
Paint Coverage CalculatorhomArea of a Rectangle CalculatorgeoFlooring CalculatorfloRoofing Shingle CalculatorhomFrench Drain Gravel Calculatorhom

In this category

Embed

Quanta Pro

Paid features are coming later.

  • All 1560 calculators remain free
  • No billing is enabled
Coming soon