How this works
Drywall (also called gypsum board, plasterboard, sheetrock or plâtre cartonné depending on the country) is sold in standard sheet sizes that vary by region. The dominant North American sheet is 4 ft × 8 ft (1.22 × 2.44 m) for residential work, with 4 × 10 and 4 × 12 used in larger commercial jobs to reduce the number of seams. European boards are typically 1.2 m × 2.4 m, 1.2 m × 2.5 m or 1.2 m × 3.0 m. Thicknesses are 1/2" (12.5 mm) for most walls, 5/8" (15 mm) for fire-rated and ceiling applications, and 1/4" (6.5 mm) for curved walls and skim-coat work. The math is the same as flooring or paint: compute the wall area, subtract doors and windows, divide by sheet area, add waste.
Waste with drywall is meaningful. The standard 10% allowance covers off-cuts at corners, around outlets and switches, around windows and doors, and the inevitable mistakes. For complex rooms with lots of cutouts (kitchens, bathrooms, rooms with built-ins), bump to 15%. For new construction with simple rectangular rooms, you can sometimes drop to 5-7%. Hanging drywall horizontally generally reduces the linear footage of seams (one long horizontal seam per wall instead of multiple vertical seams between sheets), which speeds the finishing work and produces a stronger wall — most pros hang horizontally for both reasons. Hanging vertically wastes less material on tall walls but takes longer to finish.
Three practical points. (1) Beyond sheets, you need screws (about 4-5 lbs of 1-1/4" or 1-5/8" coarse-thread screws per 1000 sq ft), joint compound (about 1 box of all-purpose mud per 8-10 sheets — ready-mix in plastic buckets is the standard for DIY), and tape (typically paper tape; figure ~250 ft of tape per 1000 sq ft of drywall). The calculator gives sheet counts; the supply estimates above scale linearly with sheet count. (2) Always measure the actual room before relying on framed dimensions — out-of-square corners and bowed studs are common, and a 12-foot wall is often 11'10½" or 12'1" in practice. Round room dimensions up to the next half-foot for material estimating. (3) For ceilings specifically, plan the layout to put seams over joists/strapping, not in the middle of bays. This usually means the long axis of the sheets runs perpendicular to the joists, and the calculator assumes you'll do that.
The formula
L, W, H are room length, width and ceiling height. Doors use 1.8 m² (≈ 19 sq ft) and windows 1.4 m² (≈ 15 sq ft) by default — both editable in advanced mode. Sheet dimensions default to 4 ft × 8 ft (1.22 × 2.44 m) but the calculator accepts any size. The "include ceiling" option adds length × width to the net area. The waste allowance is on top of the area, not on the sheet count, so partial sheets get rounded up to whole sheets after the 10% margin is applied.
Example calculation
- 12 ft × 10 ft × 8 ft room with 1 door, 2 windows, ceiling included, 4 × 8 sheets, 10% waste.
- Wall area = 2 × (12+10) × 8 = 352 sq ft. Less 1×19 + 2×15 = 49 → 303 sq ft net wall.
- Plus ceiling 12 × 10 = 120 sq ft → 423 sq ft total. With 10% waste = 465 sq ft.
- Sheets = ceil(465 / 32) = ceil(14.5) = 15 sheets.
Frequently asked questions
Should I include the ceiling?
Include it if you're hanging drywall on the ceiling — most full-room jobs do, since it's much harder and more expensive to add ceiling drywall later than to do it during the wall job. The math is simple: ceiling area = length × width, added to the net wall area. Ceiling drywall is heavier work (gravity is not your friend) and uses 5/8" thick board for fire-rating in most modern construction; it's worth knowing whether your local code requires the thicker board. Sloped or vaulted ceilings have more surface area than the floor footprint below them — measure the actual slope length, not the floor footprint, or you'll under-buy. The calculator above includes the ceiling when toggled on.
How many screws and how much joint compound do I need?
Rule of thumb per 1,000 sq ft (≈ 90 m²) of drywall: ~4-5 lbs (~2 kg) of 1-1/4" or 1-5/8" coarse-thread drywall screws (about 600-700 screws), one 5-gallon (20 L) bucket of all-purpose pre-mixed joint compound, and ~250 ft (~75 m) of paper or fibreglass mesh tape. Screws are spaced ~7 inches (18 cm) on field studs, ~12 inches (30 cm) on edges. The bucket of mud will get you through both the bedding coat over tape and the second skim; for show-quality finishes a third coat of topping mud is standard, which roughly doubles the mud quantity. For ceilings or fire-rated assemblies, switch to 1-5/8" screws and check whether your local code requires a specific spec mud (Type X assemblies sometimes do).
Hang horizontally or vertically?
Horizontal in almost every modern residential context. Hanging the long axis of the sheet horizontally produces fewer linear feet of seams to tape and finish (typically one long horizontal seam per wall instead of multiple vertical seams between adjacent sheets), and the seam falls at a comfortable height (~4 ft above the floor on an 8-ft wall) where it's easier to feather and sand. Horizontal hanging also bridges studs, producing a slightly stronger wall that resists racking better. Vertical hanging is appropriate when you have very tall walls (over 8 ft) where horizontal would leave an awkward narrow strip at top or bottom, or when working alone (vertical sheets are easier to manage solo since you only lift one end at a time). For commercial work and fire-rated assemblies, follow the assembly's tested orientation — many fire-rated UL designs specify horizontal, vertical, or either explicitly.