Should I subtract doors and windows?

For a quick estimate, no — the waste allowance usually absorbs them. For a tighter buy, subtract roughly 21 ft² (2 m²) per standard door and roughly 15 ft² (1.4 m²) per standard window from the wall area before counting sheets.

What waste allowance should I use?

10–15% is standard for a rectangular room with few openings. Bump to 15–20% if the layout is irregular, has many cutouts (windows, outlets, vents), or you are inexperienced with cutting drywall cleanly.

Which sheet size should I pick?

In the US, 4 × 8 ft is the default and easiest for one person to handle. 4 × 10 ft and 4 × 12 ft reduce horizontal seams on long walls but are heavier. In Europe, 1200 × 2400 mm is the equivalent default; 1200 × 3000 mm suits taller walls.

What thickness of drywall do I need?

1/2 in (12.5 mm) is the standard for interior walls. Use 5/8 in (15 mm) for ceilings, party walls, and any wall with a fire-rating requirement. Wet-area boards (green or blue) go in bathrooms and laundries.

Does this include screws, tape, and joint compound?

No — this calculator counts boards only. As a rough rule of thumb, allow about 30 screws per 4 × 8 ft sheet, one roll of paper or mesh tape per 7–10 sheets, and a 5-gallon bucket of joint compound per 12–15 sheets.

CONConstruction & DIY

Drywall Calculator

Estimate how many drywall sheets you need for a room. Enter room dimensions, ceiling height, sheet size, and waste allowance to get the total wall area, optional ceiling area, and the exact number of sheets to buy.

Units

Switch between metric (m, m²) and imperial (ft, ft²).

Room Length

Room Width

Ceiling Height

Sheet Size

Waste Allowance(optional)

Include Ceiling

Try an example

Enter values above to see results

How It Works

Formula

A_w = 2(L + W)\,H

A_c = \begin{cases} L \cdot W & \text{if ceiling included} \\ 0 & \text{otherwise} \end{cases}

A = A_w + A_c

N = \left\lceil \frac{A}{A_s} \cdot \left(1 + \frac{w}{100}\right) \right\rceil

Where

$L$: Room length(m)
$W$: Room width(m)
$H$: Ceiling height(m)
$A_w$: Wall area (perimeter × height)(m²)
$A_c$: Ceiling area (zero if not included)(m²)
$A$: Total drywall area(m²)
$A_s$: Area of one sheet(m²)
$w$: Waste allowance(%)
$N$: Sheets to buy (rounded up)

Enter room length, width, ceiling height, sheet size, and waste allowance. The calculator computes wall area as perimeter × height, optionally adds the ceiling, multiplies the total by (1 + waste %), divides by the sheet area, and rounds up to whole sheets.

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