Drywall calculator

How many sheets for a rectangular room, worked out two ways: by area, and by the way the sheets are actually hung. The two answers bracket what you should order.

Sheets of 4×8 drywall

16 to 17

440 sq ft to cover: 352 of wall, less 32 of openings, plus 120 of ceiling. Each sheet is 32 sq ft.

Estimate	Result	Method
By area	16 sheets	net area × 110% ÷ 32 sq ft, rounded up
By hanging layout	17 sheets	walls 12 + ceiling 5: sheets laid horizontally course by course, openings not deducted
Joint tape	205 ft	seams, butt joints and inside corners from the layout, plus 10%
Screws	about 450	rule of thumb: roughly one per square foot of board

The two methods

By area

wall area = 2 × (length + width) × height. Subtract the doors and windows, add the ceiling (length × width) if you are boarding it, add a waste percentage, and divide by the area of one sheet: 32 sq ft for 4 × 8, 40 for 4 × 10 and 48 for 4 × 12. Round up. This is the method most calculators use, and it tends to run low, because it assumes every offcut finds a home.

By hanging layout

Sheets are hung horizontally in 4 ft courses. A wall 8 ft high takes two courses; a wall 9 ft high takes three, the top one ripped. For each wall, courses × wall length / sheet length, rounded up, is the number of sheets, which lets an offcut from one course finish the next course on the same wall. The ceiling is counted the same way, with courses running along the room's length. Openings are not deducted. This is closer to how a hanger estimates a room, and it tends to run high.

Joint tape is measured from the same layout: the long seam between each pair of courses, a butt joint wherever a course needs more than one sheet, the four inside corners, and, with a ceiling, the ceiling seams and the angle where the walls meet it, plus 10%.

Worked example

A 12 × 10 ft room with 8 ft walls, one door (20 sq ft) and one window (12 sq ft), ceiling included, in 4 × 8 sheets:

Walls: 2 × (12 + 10) × 8 = 352 sq ft, less 32 for the openings = 320 sq ft
Ceiling: 12 × 10 = 120 sq ft, for 440 sq ft in total
Area method: 440 × 1.10 = 484, divided by 32 = 15.1, so 16 sheets
Layout method: each 12 ft wall is two courses of 12 ft, 24 ft of sheet, 3 sheets; each 10 ft wall is 20 ft, 2.5, so 3 sheets; that is 12 for the walls. The ceiling is three courses of 12 ft, 36 ft, 5 sheets. Total 17.

So order 16 or 17 sheets. With 4 × 12 sheets both methods agree on 11, and there are fewer butt joints to finish.

The same room with each sheet size

Sheet	By area	By layout	Tape
4 × 8 ft	16	17	205 ft
4 × 10 ft	13	14	188 ft
4 × 12 ft	11	11	159 ft

Where it stops being reliable

Rectangular rooms only. Closets, bulkheads, sloped ceilings, stairwells and outside corners need their own allowance. For an L-shaped room, split it into rectangles, remember that shared walls are not walls, and add up the parts.
Screws are a rule of thumb. About one per square foot is a common planning figure; the real count depends on framing spacing and the fastening schedule required for your assembly.
No compound estimate. Coverage depends on the product and the finisher, so the honest source is the bag or bucket you are buying.
Code requirements are not checked. Fire-rated assemblies, moisture-resistant board in wet areas and ceiling thickness over wide framing are set by your local building code.

Common questions

Why are there two different sheet counts?

Because there are two honest ways to estimate. The area method divides the surface by the area of a sheet and adds a waste percentage; it deducts doors and windows. The layout method counts sheets the way they are hung, course by course along each wall, and deducts nothing, because the piece cut out for a window is rarely big enough to use elsewhere. The truth is usually between them. Buying the higher number, or one or two sheets over the lower one, is the usual compromise.

Should I hang drywall horizontally or vertically?

On ordinary 8 ft walls, horizontal hanging usually gives fewer and shorter seams, and the long tapered joint sits at a comfortable height for finishing. Vertical hanging suits tall walls and some commercial work, and some fire-rated assemblies specify it. The layout method here assumes horizontal courses.

Are longer sheets better?

Fewer butt joints, which are the hardest seams to finish flat, and often fewer sheets. But 12-foot sheets are heavy (a 1/2-inch 4×12 weighs very roughly 55 to 80 pounds, depending on whether it is a lightweight or standard product) and awkward up stairs and through doors. Use the longest sheet that suits the wall lengths and that you can get into the room.

What thickness do I need?

Half-inch board is standard for walls in houses. Five-eighths is common on ceilings, especially with framing at 24 inches on center, and 5/8-inch Type X fire-rated board is required by building codes in certain places, such as some walls and ceilings between a garage and the living space. Check the rules that apply where you live.

How much joint compound will I need?

It varies too much with the compound type, the number of coats and the finisher to give one honest figure, so this calculator does not guess. The tape length is a better starting point: ask your supplier, or read the coverage figure printed on the compound you are buying.