How the drywall calculator works
The tool finds the surface to be boarded, adds a cutting allowance and divides by the face area of one sheet. Drywall (plasterboard in the UK and Europe) is always bought in whole sheets, so the result is rounded up.
Sheets = ⌈ (2 × (L + W) × H − openings + ceiling) × 1.10 ÷ sheet area ⌉Doors are deducted at 1.9 m² (21 ft²) and windows at 1.4 m² (15 ft²). The 10% covers offcuts around openings, sockets and corners. Consumables are estimated from the boarded area with ratios taken from manufacturer installation guides: about one screw per square foot of board (10–11 per m²), 0.37 ft of paper tape per ft² (1.2 m per m²) and 0.14 lb of ready-mixed all-purpose compound per ft² (about 0.68 kg per m²) for a three-coat finish.
Worked example
A 4 m × 3.5 m room with 2.5 m walls has 37.5 m² of wall. One door and one window leave 34.2 m². With the 10% allowance that is 37.6 m², and 1.2 × 2.5 m sheets are 3.0 m² each, so 37.6 ÷ 3.0 = 12.5 rounds up to 13 sheets. Thirteen sheets need about 420 screws, 41 m of tape and roughly 23 kg of joint compound, a little over one 20 kg tub or 1.5 buckets of 15 kg. Boarding the 14 m² ceiling as well lifts the total to 48.2 m² and 18 sheets.
Standard sheet sizes and weights
| Sheet | Area | Thickness | Approx. weight |
|---|---|---|---|
| 4 × 8 ft | 32 ft² | 1/2 in (12.7 mm) | 50–57 lb (lightweight: 38–44 lb) |
| 4 × 12 ft | 48 ft² | 1/2 in | about 75–85 lb |
| 4 × 8 ft Type X | 32 ft² | 5/8 in (15.9 mm) | about 70 lb |
| 1.2 × 2.4 m | 2.88 m² | 12.5 mm | about 25–28 kg |
| 1.2 × 2.5 m | 3.0 m² | 12.5 mm | about 26–30 kg |
| 1.2 × 3.0 m | 3.6 m² | 12.5 mm | about 32–36 kg |
12.5 mm (1/2 in) is the usual wall board. Ceilings on joists at 600 mm or 24 in centres call for 15 mm or 5/8 in to avoid sagging, and fire-rated, moisture-resistant or acoustic boards are specified where building rules demand.
Hanging tips that change the numbers
- Longer sheets mean fewer joints. A 4×12 ft sheet laid horizontally spans a whole 12 ft wall with no butt joint, which saves the hardest taping work, but it is a two-person lift.
- Screw spacing. Typical spacing is 12 in (300 mm) in the field on walls and 7–8 in (200 mm) on ceilings; ceilings therefore use more screws than the average above.
- Use 1-1/4 in (32 mm) coarse-thread screws for 1/2 in board on wood studs and fine-thread screws for steel studs; the head should dimple the paper without tearing it.
- Stagger the joints so that end joints do not line up on the same stud across neighbouring rows.
- Fire and wet areas such as garages next to living space, or showers, follow specific local rules; check them or ask a qualified installer before you buy board.
Frequently asked questions
How many sheets of drywall do I need for a 12×12 room?
The walls of a 12 × 12 ft room with 8 ft ceilings total 384 ft². After one door and one window and with 10% waste you need 12 sheets of 4×8, or 17 including the 144 ft² ceiling.
How many screws per sheet of drywall?
Plan on about 32 screws for a 4×8 sheet on walls, roughly one per square foot. Ceilings with closer spacing take 40 or more per sheet.
How much joint compound do I need per sheet?
Around 0.14 lb per square foot, so about 4.5 lb per 4×8 sheet for three coats. A 4.5 gallon bucket of all-purpose compound finishes roughly 13 sheets.
Is 4×8 or 4×12 drywall better?
4×12 sheets create fewer butt joints and less taping on long walls, but they are heavy and hard to carry upstairs. 4×8 sheets suit small rooms, stairwells and one-person jobs.
What size is plasterboard in Europe?
The common sizes are 1.2 × 2.4 m, 1.2 × 2.5 m, 1.2 × 2.6 m and 1.2 × 3.0 m, usually 12.5 mm thick. Some markets also sell narrower 0.9 m or 0.6 m boards for easier handling.
Last reviewed: 2026-09-27 · How we calculate