# How much drywall should I buy?

Computes how many sheets of drywall (sheetrock, gypsum board) cover a room’s walls, and its ceiling if chosen, less doors and windows, with an extra share for waste.

- Page: https://www.acalculator.org/construction/drywall-calculator
- JSON spec: https://www.acalculator.org/construction/drywall-calculator.json
- Version: 1bb94acbed83

## Default answer

Example with the default inputs (Room length 12 ft, Room width 14 ft, Wall height 8 ft, Sheet size 4 × 8 ft, Extra for waste 10%, Doors 1, Area of one door 20 ft², Windows 2, Area of one window 15 ft², Cover the ceiling too No): For 366 ft² of drywall, the sheets to buy come to 13 (12.58 before rounding up).

## Inputs

| Key | Label | Description |
| --- | --- | --- |
| l | Room length | The length of the room, wall to wall. |
| w | Room width | The width of the room, wall to wall. |
| h | Wall height | The height of the walls, floor to ceiling. |
| sheet | Sheet size | The size of one drywall sheet. |
| extra | Extra for waste | Drywall to add, in percent, for cut-offs around openings and at the ends of walls. |
| doors | Doors | How many doors are in the walls. |
| da | Area of one door | The area of one door opening: 20 ft² for 36 × 80 in. |
| win | Windows | How many windows are in the walls. |
| wa | Area of one window | The area of one window opening: 15 ft² for 3 × 5 ft. |
| ceil | Cover the ceiling too | Whether to add the ceiling (length × width) to the area. |

## Outputs

| Key | Label | Description |
| --- | --- | --- |
| sheets | Sheets to buy | The area with extra ÷ the area of one sheet, rounded up to whole sheets. |
| exactSheets | Sheets, not rounded | The area with extra ÷ the area of one sheet, before rounding up. |
| squareFeet | Area to cover, ft² | The wall area less doors and windows, plus the ceiling if chosen, before the extra. |
| squareMeters | Area to cover, m² | The same area in square metres. |

## Method

Area = 2 × (length + width) × height − doors × door area − windows × window area (+ length × width for the ceiling); sheets = area × (1 + extra ÷ 100) ÷ sheet area, rounded up.

## Assumptions

- The room is a rectangle with walls of one height; door and window openings are not covered.
- By default a door opening is 20 ft² (36 × 80 in) and a window 15 ft² (3 × 5 ft).
- Extra for waste is 10% by default, for cut-offs around openings and at wall ends.
- Sheets are counted by area; the count does not plan where each seam falls.

## Worked examples

1. l = 3.6576, w = 4.2672, h = 2.4384, sheet = 4x8, extra = 10%, doors = 1, da = 1.858061, win = 2, wa = 1.393546, ceil = no gives squareFeet = 366, exactSheets = 12.58125, sheets = 13. Source: NIST Handbook 44, Appendix C (1 ft = 0.3048 m).
2. l = 3.6576, w = 3.6576, h = 2.4384, sheet = 4x12, extra = 0%, doors = 0, da = 1.858061, win = 0, wa = 1.393546, ceil = yes gives squareFeet = 528, exactSheets = 11, sheets = 11. Source: 2 × 24 × 8 + 144 = 528 ft² ÷ 48 = 11 sheets (NIST Handbook 44 units).
3. l = 4, w = 3, h = 2.5, sheet = 1200x2400, extra = 10%, doors = 1, da = 1.8, win = 1, wa = 1.5, ceil = no gives squareMeters = 31.7, exactSheets = 12.107639, sheets = 13. Source: 2 × 7 × 2.5 − 1.8 − 1.5 = 31.7 m² × 1.1 ÷ 2.88 = 12.11, so 13 sheets (NIST Handbook 44 units).

## FAQ

### How do I calculate how much drywall I need?

Find the wall area: 2 × (length + width) × height. Subtract doors and windows, add the ceiling if you are covering it, add about 10% for waste, and divide by the area of one sheet. A 12 × 14 ft room with 8 ft walls, one door and two windows has 366 ft²; 366 × 1.1 ÷ 32 = 12.58, so 13 sheets of 4 × 8 ft.

### How many square feet are in a sheet of drywall?

Width × length: a 4 × 8 ft sheet is 32 ft², 4 × 10 ft is 40 ft², 4 × 12 ft is 48 ft², and a 54 in × 12 ft sheet is 54 ft². A metric 1200 × 2400 mm sheet is 2.88 m² (31.0 ft²).

### Should I use 4 × 8 or 4 × 12 sheets?

Longer sheets mean fewer seams to tape on long walls and ceilings, but they are heavier and harder to carry. The count by area is about the same; pick the size you can handle and that fits your walls. 54 in wide sheets suit 9 ft walls with fewer seams.

### How much extra drywall should I buy?

The calculator adds 10% by default for pieces cut off around doors, windows and wall ends. A room with many openings, angles or short walls may need more. Set the extra to 0% for the covered area alone.

### Do I subtract doors and windows?

Yes. The calculator takes 20 ft² for each door (36 × 80 in) and 15 ft² for each window (3 × 5 ft) by default; type your own sizes for a closer answer. Small openings are often covered and cut out later, so some builders do not subtract them.

### How do I include the ceiling?

Turn on “Cover the ceiling too”. The calculator adds length × width. A 12 × 12 ft room with 8 ft walls and the ceiling is 384 + 144 = 528 ft², exactly 11 sheets of 4 × 12 ft with no extra.

## Sources

- NIST Handbook 44 (2024), Appendix C, General Tables of Units of Measurement: 1 ft = 12 in = 0.3048 m; 1 ft² = 144 in². https://www.nist.gov/pml/owm/nist-handbook-44-current-edition
- OpenStax, Prealgebra 2e, §9.4 Use Properties of Rectangles, Triangles, and Trapezoids (area and perimeter of a rectangle). https://openstax.org/books/prealgebra-2e/pages/9-4-use-properties-of-rectangles-triangles-and-trapezoids