Drywall worked example: 4 m x 3 m room, 2.4 m ceiling

BuildTrue drywall pack. Estimates only. This example uses the same formulas as the drywall calculator on the pack page and the standalone BuildTrue drywall estimator. Verified by hand, step by step, below.

Inputs

Input	Value
Room length	4 m
Room width	3 m
Ceiling height	2.4 m
Ceiling boarded	Yes
Door opening deducted	0.9 m x 2.0 m = 1.8 sq m
Window opening deducted	1.2 m x 1.0 m = 1.2 sq m
Sheet size	4 x 8 ft (32 sq ft)
Waste allowance	10 percent
Conversion, stated	1 sq m = 1 / 0.09290304 sq ft = 10.7639 sq ft

Step by step arithmetic

1. Wall perimeter:

4 + 3 + 4 + 3 = 14 m.

1. Gross wall area:

14 m x 2.4 m = 33.6 sq m.

1. Ceiling area:

4 m x 3 m = 12.0 sq m.

1. Gross area:

33.6 + 12.0 = 45.6 sq m.

1. Openings deducted:

1.8 + 1.2 = 3.0 sq m. Net area = 45.6 - 3.0 = 42.6 sq m. This net figure, 42.6, is the number entered in the calculator.

1. Net area in square feet:

42.6 / 0.09290304 = 458.54 sq ft, shown as 458.5 sq ft.

1. Area with waste:

458.54 x 1.10 = 504.40 sq ft, shown as 504.4 sq ft. In metric: 42.6 x 1.10 = 46.86 sq m.

1. Sheets:

504.40 / 32 = 15.7625 sheets. Round up with the epsilon safe ceiling: 16 sheets. Sanity check: 15 sheets x 32 = 480 sq ft, short of 504.4. 16 x 32 = 512 sq ft, which covers it.

1. Screws, using the stated guide of 32 screws per 4 x 8 ft sheet:

16 x 32 = 512 screws.

1. Joint compound, using the stated guide of 1 box per 400 sq ft of board area:

504.40 / 400 = 1.261 boxes. Round up: 2 boxes.

Purchasable counts

Item	Raw result	Buy
Drywall sheets, 4 x 8 ft	15.76 sheets	16 sheets
Drywall screws	512 screws	A box or pail totalling at least 512 screws
Joint compound, 4.5 gallon box size in the guide	1.26 boxes	2 boxes
Joint tape	Not produced by the sheet formula	Estimate from total joint length on the layout
Corner bead	Not produced by the sheet formula	Count outside corners on site

Sample material list for this job

Item	Specification	Quantity
Drywall sheets	4 x 8 ft	16
Drywall screws	Length suited to board and framing	At least 512 count
Joint compound	4.5 gallon box	2
Joint tape	Paper or mesh, one system	Per joint length on layout
Corner bead	As specified	Per outside corner count on site

Notes and limits

• Deducting openings is a choice, not a rule. Many estimators order on gross area for small rooms because the offcuts get used around the openings anyway. This example deducts, and says so, so the arithmetic can be checked. Either way, state your choice on the quote.
• If the same job used 4 x 12 ft sheets (48 sq ft): 504.40 / 48 = 10.51, rounded up to 11 sheets, and screws at 48 per sheet = 11 x 48 = 528 screws.
• Estimates only. Finish level, layout, and ceiling height change real needs. Verify before ordering, and confirm local code and permit requirements where they apply.