How much drywall do I need for a room?

People type this into search every day: how much drywall do I need.

The usual answer is “a 4 by 8 sheet covers 32 square feet.” That is the panel. It is not the order. Walls have height. Doors punch holes. Offcuts do not go back on the wall.

This page is a labeled example. It is not a hanging spec, and it is not a fire-rating or wet-area schedule.

Wall area first, then waste, then sheets

USG’s Sheetrock installation and finishing guide (J371) is the method I am using. Measure length and height for each wall, then multiply to get square footage. Subtract large openings such as doorways and picture windows. Skip electrical boxes and pipe fittings. Do the same for the ceiling. Total the figures, then read the sheet count from their coverage table.

That table lists 4 ft by 8 ft panels at 32 sq. ft. each. Fifteen of those cover 480 sq. ft. Fourteen cover 448 sq. ft. A 4 by 10 panel is 40 sq. ft. A 4 by 12 panel is 48 sq. ft.

Georgia-Pacific’s drywall calculator adds a different rule on top. It “automatically adjusts for 10% in cut-outs and waste.” CertainTeed’s drywall calculator tells you not to subtract windows, doors, or outlets, and says its estimate does not include waste.

Three manufacturers, three leftovers. The drywall sheet quantity calculator follows USG on openings and Georgia-Pacific on a typed waste line:

(perimeter × height − openings) × (1 + waste) ÷ sheet area

Then it rounds up to the next whole sheet. Only wall surfaces are included. Sheet orientation and offcuts may change the yield. Those are the tool’s assumptions.

The default sheet is 2.88 m². That is a 1.2 m by 2.4 m metric panel. On a US display it shows as 31 ft², next to USG’s 32 sq. ft. 4 by 8. Type the size printed on the stack you will buy.

The published 15-sheet room

Here are the calculator defaults:

• room perimeter: 18 m
• wall height: 2.5 m
• doors and windows: 6 m²
• area per sheet: 2.88 m²
• waste allowance: 10%

Wall rectangle: 18 × 2.5 = 45 m²

Net wall area: 45 − 6 = 39 m²

Area with waste: 39 × 1.10 = 42.9 m²

Sheets: 42.9 ÷ 2.88 = 14.90, rounded up to 15 sheets

On a US display those areas are 484.4 ft², 419.8 ft², and 461.8 ft². The 18 m perimeter is 59.06 ft. The 2.5 m height is 8.2 ft. The 6 m² of openings is 64.6 ft².

That 18 m perimeter is a 5 m by 4 m rectangle, so the floor is 20 m². The square footage calculator prints 20 m² / 215.3 ft² when you put 5 m by 4 m in room 1 and zero the other rooms. Buy drywall from the floor figure and you order 20 × 1.10 ÷ 2.88 = 7.64, rounded up to 8 sheets. You would be short 7 sheets.

USG’s table would cover 419.8 ft² of net wall with 14 of the 4 by 8 panels (448 sq. ft.). The 10% waste line pushes the order to 461.8 ft², which needs the 15th sheet (480 sq. ft.). That extra panel is the Georgia-Pacific 10% habit sitting on USG’s opening subtraction.

5% and 10% can buy the same sheets

Hold 18 m, 2.5 m, 6 m² of openings, and 2.88 m² sheets. Change only waste.

• 0% waste: 39 m², 419.8 ft², 14 sheets
• 5% waste: 41 m², 440.8 ft², 15 sheets
• 10% waste (default): 42.9 m², 461.8 ft², 15 sheets
• 15% waste: 44.8 m², 482.8 ft², 16 sheets

5% and 10% land on the same count because 41 ÷ 2.88 and 42.9 ÷ 2.88 both sit under 15 after the ceiling. Area still moves. Sheets do not, until 15% crosses the next panel.

Georgia-Pacific’s 10% is a planning allowance their calculator applies. It is not a building code. CertainTeed’s public tool leaves waste out and tells you to check local code. I am not going to pick a waste number for a stairwell or a room full of windows. Type the leftover you expect.

Sheet size is the other lever

USG’s three common panels, converted so the calculator can take them, on the same 42.9 m² order:

• 2.88 m² default (about 31 ft²): 15 sheets
• 2.973 m² (4 ft by 8 ft = 32 ft²): 15 sheets
• 3.716 m² (4 ft by 10 ft = 40 ft²): 12 sheets
• 4.459 m² (4 ft by 12 ft = 48 ft²): 10 sheets

The 4 by 8 size still buys 15 because 42.9 ÷ 2.973 = 14.43, and the tool ceilings that leftover. The 4 by 10 and 4 by 12 sizes drop the count because each panel is larger, not because the wall got smaller.

Taller sheets reduce joints on a 2.5 m wall. They also need a second person and a longer van. The card will still do the division either way.

Height moves the count more than a small waste tweak

Hold 18 m, 6 m² of openings, 10% waste, and 2.88 m² sheets. Change only height.

• 2.4 m: net 37.2 m², with waste 40.9 m², 15 sheets
• 2.5 m (default): 39 m² / 42.9 m², 15 sheets
• 3.0 m: net 48 m², with waste 52.8 m², 19 sheets

2.4 m still buys 15 sheets. 40.9 ÷ 2.88 = 14.20, and the ceiling keeps the 15th panel. 3.0 m is 0.5 m extra. That 20% taller wall adds 52.8 − 42.9 = 9.9 m² and 4 sheets.

A 4 m by 3 m room is a 14 m perimeter. Keep 2.5 m height, drop openings to 4 m², keep 10% and 2.88 m² sheets.

Net: 14 × 2.5 − 4 = 31 m² (333.7 ft²)

With waste: 34.1 m² (367 ft²)

Sheets: 12

A 6 m by 5 m room is a 22 m perimeter. Openings 8 m².

Net: 22 × 2.5 − 8 = 47 m² (505.9 ft²)

With waste: 51.7 m² (556.5 ft²)

Sheets: 18

12 sheets and 18 sheets are different van loads. The formula is the same walk around the room.

Ceilings use floor area. Paint uses the same walls.

USG says to do the ceiling the same way you did the walls. The drywall tool does not add a ceiling field. The ceiling is close to the floor rectangle.

On this 5 m by 4 m room that floor is 20 m². Add it to the 39 m² of net wall and you have 59 m². With 10% waste: 64.9 m². At 2.88 m² per sheet: 64.9 ÷ 2.88 = 22.53, rounded up to 23 sheets. That 23 is the walls plus the ceiling. It is not what the wall-only card prints.

The paint quantity post is the same wall rectangle after the board is up. On these defaults, painted wall area is still 39 m². Two coats at 10 m²/L:

39 × 2 ÷ 10 = 7.8 L, rounded up to 8 L (2.1 gal on a US display)

The flooring post is waste-then-packs on the floor. The concrete post is the same habit with depth. Drywall adds height and a sheet size.

Open the drywall sheet quantity calculator with the perimeter you walked, the height you measured, and the sheet size on the stack. Subtract only the doors and windows you will skip. If the next job is paint, use the paint quantity calculator on the same walls. If you need the floor number for a ceiling, use the square footage calculator.