Drywall Calculator

How to use this calculator

Add up the lengths of the walls you are covering to get the perimeter, then enter the wall height. Include the ceiling area if you are hanging it too, and subtract doors and windows (a standard door is about 21 ft², a typical window 12–15 ft²). Pick the sheet size: longer sheets mean fewer butt joints to tape but are heavier to handle.

The 10% default waste allowance covers off-cuts around openings and corners. Use 15% for rooms with many small walls, soffits or angled ceilings. Run the calculator backwards to see how much wall area a stack of sheets will cover.

The formula

A_walls = P × h

A_net = A_walls + A_ceil − A_open

N = A_net × (1 + w%) / A_sheet

P: room perimeter (sum of wall lengths)
h: wall height
A_walls: wall area
A_ceil: ceiling area (0 if not hanging the ceiling)
A_open: doors & windows area
A_net: area to cover
w%: waste allowance
N: sheets needed

Worked example

A 12 × 12 ft bedroom with 8 ft walls is being hung with 4 × 8 sheets on walls and ceiling. There is one door and one window.

Wall area = perimeter × height = 48 × 8 = 384 ft²; ceiling = 12 × 12 = 144 ft².
Area to cover = 384 + 144 − 40 (door and window) = 488 ft².
Sheets = 488 × 1.10 ÷ 32 = 16.8, rounded up to 17 sheets.

Order 17 sheets of 4 × 8 board. Hanging the ceiling with 4 × 12 sheets instead cuts joints and saves about two sheets.

Rules of thumb for materials

Screws: about one per square foot of board on walls with studs 16 in on center (roughly 32 per 4 × 8 sheet), a little more on ceilings.
Joint compound: around 0.05 gallon per square foot for three coats of ready-mixed compound on taped joints.
Ceilings over 16 in joist spacing need ⅝-inch board or ½-inch sag-resistant ceiling board.

These are planning estimates; follow the board and compound manufacturer’s instructions.

Assumptions and limits

Sheet counts are based on area. Very tall walls or rooms with many short wall segments produce more off-cuts than the allowance assumes.
Board thickness does not change the sheet count, only the weight and fastener length.

Frequently asked questions

How many sheets of drywall for a 12 × 12 room?

With 8 ft walls, the walls alone are 384 ft²: about 12 sheets of 4 × 8 after openings and 10% waste. Adding the ceiling brings it to about 17.

Should I hang drywall horizontally or vertically?

On walls up to 8 ft high, horizontal hanging usually means fewer joints and puts the seam at a comfortable working height. Commercial codes sometimes require vertical hanging for fire-rated assemblies.

Do I subtract doors and windows?

Yes for large openings. Many pros ignore small windows, because the cut-out pieces are rarely usable and the extra board offsets waste.