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Drywall Calculator

Find how many drywall sheets a room's walls and ceiling need after doors and windows, plus typical amounts of screws and joint compound.

Level: Grades 6–7

  • Common Core standard 7.G.B.6Solve real-world and mathematical problems involving area, volume and surface area of two- and three-dimensional objects composed of triangles, quadrilaterals, polygons, cubes, and right prisms.
Printable worksheet

Drywall Calculator

Inputs

A standard interior door opening is about 3 ft × 7 ft.

Sheet size

Extra for offcuts and damaged sheets. 10% is common; use 15% for rooms with many corners and openings.

Typical: about 1 per ft², roughly 32 per 4 × 8 sheet. Ceilings often use a little more.

Typical: about 1 gallon of ready-mixed compound per 100 ft² for taping and two finish coats. Check your product.

Result

4 × 8 ft sheets to buy

16

Buy about 16 sheets of 4 × 8 ft drywall, around 512 screws and 4.4 gallons of joint compound.

Sheets for the walls
11
Sheets for the ceiling
5
Area to cover
439 ft²
Net wall area
319 ft²
Screws (typical rate)
512
Joint compound (typical rate)
4.39 gal

See the step-by-step solution ↓

Step-by-step solution

  1. Find the total wall area: the distance around the room, 2 × (length + width), times the wall height

    2×(12+10)×8=352 ft²

  2. Take away the doors and windows, since they don't get drywall

    352−1×3×7−1×3×4=319 ft²

  3. Add 10% for waste, divide by the 32 ft² one 4 × 8 ft sheet covers, and round up to whole sheets

    319×1.132=10.9656=rounded up:11

  4. Find the ceiling area: length × width

    12×10=120 ft²

  5. Count ceiling sheets on their own, because leftover wall pieces rarely fit the ceiling

    120×1.132=4.125=rounded up:5

  6. Add the wall and ceiling sheets to get the number to buy

    11+5=16

  7. Estimate screws: all the board you buy × 1 per ft². This is a typical rate, not the official screw spacing

    16×32×1=512

  8. Estimate joint compound: the area you'll finish × 1 gallons for every 100 ft² (a typical rate)

    439×1100=4.39 gal

Test yourself

20 quick questions built from this calculator's formula: work out results, predict what happens when an input changes, and work backward from an answer. Every answer comes with the working.

What this calculator does

Get your drywall shopping list: how many sheets, how many screws and how much joint compound to buy. The sheet count comes from the area of the walls, plus the ceiling if you're covering it. Doors and windows come off. Then a bit is added for offcuts, the scraps every room leaves behind.

Enter a rectangular room's length, width and wall height. The calculator takes away the openings you list and divides by the area of your chosen sheet size. Walls and ceiling are rounded up separately, because scraps from one rarely fit the other. It then uses typical rates for screws and ready-mixed joint compound. Every number is an estimate to help you plan a purchase. It doesn't replace your local building code or the board maker's instructions.

Where it's used

Why this math matters outside the classroom:

  • Bedroom walls. A 12 × 10 ft room with 8 ft walls has 2 × 22 × 8 = 352 ft² of wall before doors and windows are subtracted.
  • Sheet counts. Dividing 320 ft² of wall by 32 ft² per 4 × 8 sheet gives 10 sheets before any waste allowance.
  • Ceilings. A 12 × 10 ft ceiling is 120 ft², or 3.75 sheets, so it takes 4 sheets of 4 × 8 board.
  • Basement finishing. Homeowners finishing a basement add up every wall and ceiling surface to order sheets, screws and compound in one trip.
  • Surface area. Students find the walls and ceiling of a room as the surface area of a box with the floor left out.

Grade level and standards: Grades 6–7; Common Core State Standards for Mathematics 7.G.B.6. © Copyright 2010. National Governors Association Center for Best Practices and Council of Chief State School Officers. All rights reserved.

How to use it

  1. Enter the room's length, width and wall height in feet. Tick the box if the ceiling gets drywall too.
  2. Enter the number and size of doors and windows to take away.
  3. Choose the sheet size and how much extra to allow for waste.
  4. Change the screw and compound rates if your product or screw pattern is different. Then read the sheet count and supplies.

What the inputs mean

Door width
A standard interior door opening is about 3 ft × 7 ft.
Sheet size
Longer sheets mean fewer end-to-end seams to tape, but they're heavy and awkward. 4×8 sheets are easiest to handle alone. 4×12 sheets suit long walls and ceilings, with a helper or a lift.
Waste allowance
Covers cut-outs, scraps too small to reuse and the odd broken corner. Rooms with many openings, angles or boxed-in areas (soffits) need more.
Screws per ft² of board
A planning rate only. Screw spacing is set by the board maker and your local code. It's usually closer together on ceilings than on walls.
Joint compound per 100 ft²
Ready-mixed compound for bedding the tape plus two more coats. Powder that you mix (setting-type), thicker coats or a very smooth level 5 finish change the amount a lot.

Formula and method

wall area = 2 × (length + width) × height − doors − windows
wall sheets = wall area × (1 + waste ÷ 100) ÷ sheet area, rounded up
ceiling sheets = length × width × (1 + waste ÷ 100) ÷ sheet area, rounded up
screws ≈ sheets × sheet area × screws per ft²
joint compound ≈ (wall area + ceiling area) × gallons per 100 ft² ÷ 100

In the formulas, length, width and height are in feet, ft² means square feet, and waste is the extra percent you chose. The sheet area is how many square feet one sheet covers. The distance around the room times the wall height gives the total wall area. Each door and window takes away its width times its height. A 4 ft wide sheet covers 32, 40 or 48 ft², depending on its length.

Screws are estimated on all the board you buy, since every sheet you hang is screwed on all over. Joint compound is estimated on the area you actually finish, after openings come off.

Worked example

A 12 × 10 ft bedroom with 8 ft walls, one 3 × 7 ft door and one 3 × 4 ft window, ceiling included, using 4 × 8 sheets and 10% waste.

  1. Total wall area: 2 × (12 + 10) × 8 = 352 ft².
  2. Take away the openings: 352 − 21 − 12 = 319 ft².
  3. Wall sheets: 319 × 1.1 ÷ 32 = 10.97, rounded up to 11.
  4. Ceiling: 12 × 10 = 120 ft²; 120 × 1.1 ÷ 32 = 4.125, rounded up to 5 sheets.
  5. Screws: 16 × 32 × 1 = 512. Joint compound: 439 × 1 ÷ 100 = 4.39 gal.

Result: Buy 16 sheets of 4 × 8 drywall, roughly 512 screws and about 4.4 gallons of joint compound.

Understanding the result

The sheet count is what to order. If the ceiling sheets come out just over a whole number, a longer sheet can sometimes save you one.

Screws and compound are rounded planning numbers. Screws are usually sold by weight, so check the count per pound on the box. Compound comes in buckets or boxes of several gallons.

Assumptions and limitations

  • The room is a rectangle with walls of one height, and every wall gets drywall.
  • All doors are one size, and all windows are one size.
  • The waste allowance applies to walls and ceiling alike.
  • Sheets are counted by area, not from a layout plan. Very tall walls, stairwells and sloped ceilings need a layout drawing.
  • Tape, corner bead, glue and primer aren't included.
  • Fire-rated, moisture-resistant and ceiling boards may have their own screw rules, which local codes require you to follow.

Frequently asked questions

Should I hang drywall horizontally or vertically?

On walls up to about 8 ft tall, many installers hang sheets sideways (horizontally). That puts the long, thinner edges together in one seam at a comfortable height, and it cuts down the length of seams. The sheet count by area is the same either way.

Why are the wall and ceiling sheets rounded separately?

Ceiling pieces are cut to stretch between the framing, and they're usually hung first. So leftover wall pieces seldom fit. Rounding each surface up on its own gives a more realistic order than lumping the areas together.

How many screws does one sheet take?

A common planning number is about 32 for a 4 × 8 sheet on walls, which is the default of 1 per ft². The real spacing depends on the framing layout, the board type and the code where you live.

Do I subtract every opening?

Take away doors, windows and large openings such as pass-throughs. Small cut-outs for outlets and switches make no real difference, and the waste allowance covers them.

How this calculator is checked

Method: Rectangular room wall and ceiling areas less openings, divided by sheet area with ceiling rounding; screw and compound figures use editable typical rates. The calculation is covered by automated tests with known reference values and edge cases. Last updated 2026-10-18. Found a problem? Tell us.

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