Thickness, weight and type of gypsum board for walls, ceilings, garages and wet rooms.
Most interior walls in the US are finished in ½ in drywall, and most ceilings on wider framing and fire-separation work use ⅝ in. Thinner sheets are for curves and overlays. In the UK and Europe the same material is called plasterboard and comes in 9.5, 12.5 and 15 mm. Thickness decides how flat a wall stays and how much it weighs, and the type decides how it behaves in a fire or in a damp room. The tables below give the sizes, the weights from manufacturers' data, and the points where a building code, not a preference, sets the choice.
Weights vary by product and maker; lightweight ½ in boards are lighter still. Sheets are 4 ft wide and 8, 10 or 12 ft long (1219 × 2438 mm for a 4 × 8).
| Thickness | Metric | Weight (lb/ft²) | Weight (kg/m²) | 4 × 8 ft Sheet | Typical Use |
|---|---|---|---|---|---|
| ¼ in | 6.4 mm | 1.13 | 5.5 | 36 lb | Curves, overlaying old walls |
| ⅜ in | 9.5 mm | 1.25 | 6.1 | 40 lb | Repairs, overlaying plaster |
| ½ in | 12.7 mm | 1.60 | 7.8 | 51 lb | Standard walls and ceilings |
| ⅝ in Type X | 15.9 mm | 2.2 | 10.7 | 70 lb | Fire-rated work, ceilings at 24 in |
4 rows
Standard wallboard is EN 520 Type A. Other letters mark other properties, including F for fire and H for reduced water absorption; check the maker's sheet.
| Thickness | Weight (kg/m²) | 2400 × 1200 mm Sheet |
|---|---|---|
| 9.5 mm | 6.1 | 17.6 kg |
| 12.5 mm | 8.1 | 23.3 kg |
| 15 mm | 10.1 | 29.1 kg |
3 rows
| Board | Key Feature | Standard | Where It Goes |
|---|---|---|---|
| Regular | Gypsum core, paper faces | ASTM C1396 | Dry walls and ceilings |
| Type X | Glass fibre in the core | ASTM C1396 | Rated assemblies, garage ceilings |
| Type C | Better fire performance than Type X | ASTM C1396 | High-rating assemblies |
| Water-resistant backing | Moisture-resistant core and facing | ASTM C1396 | Damp areas, not wet ones |
| Glass-mat gypsum | No paper to feed mould | ASTM C1177 | High humidity, exterior sheathing |
| Cement backer board | Cement core | ANSI A118.9, ASTM C1325 | Tile in wet areas, with a membrane |
6 rows
A fire rating belongs to a tested assembly, not to a board. To get the rating, build the listed assembly exactly: the same board, framing, fasteners, spacing and insulation. ASTM C1396 describes ⅝ in Type X as giving 1 hour and ½ in Type X as giving ¾ hour when applied to load-bearing 2 × 4 framing. Type X and Type C cannot be swapped unless the listing allows it.
The International Residential Code asks for at least ½ in gypsum board on the garage side between a garage and a house or attic, and at least ⅝ in Type X on a garage ceiling below habitable rooms.
A ceiling sheet hangs from its fasteners, so it must be stiffer than a wall. Run sheets across the joists, and use ⅝ in or ½ in sag-resistant board at 24 in spacing. Where water-based texture will be sprayed on a ceiling, the IRC raises the minimum to ½ in at 16 in spacing and ⅝ in at 24 in, unless ½ in sag-resistant board is used.
Water-resistant gypsum board suits damp rooms, but the Tile Council of North America's guidance rules out gypsum board of any kind as a direct tile backing in wet areas. In a shower or tub surround use cement backer board or another rated backer, and add a waterproofing membrane. Cement board resists water damage but is not itself waterproof.
The walls of a room 12 by 16 ft and 8 ft high total 448 ft². With 4 × 8 ft sheets that is 448 ÷ 32 = 14 sheets, or 16 with 10% waste. In ½ in board they weigh about 800 lb, so plan how they get upstairs.
By O.E. — Partner, chairman of the board and CEO of a metal products manufacturer for 21 years; the company exports to 45 countries.
Drafted with AI assistance; calculations checked against primary sources and tested with the site's own code. About FlowUtil
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Classification: Published standards, model code and manufacturers' data
Sources
ASTM C1396 — Standard Specification for Gypsum Board
ASTM International
standard previews; full text not opened
International Residential Code, Table R302.6 and Section R702.3
International Code Council
read through published building-department handouts
Sheetrock Firecode X specification; gypsum board data sheet; wallboard data sheet
USG; CertainTeed; Knauf
weights
Tile and Stone Backer Board Selection Guide, quoting Tile Council of North America guidance
Laticrete
ANSI A118.9, ANSI A118.10 and wet-area use
Weights are manufacturers' figures and vary by product. Fire ratings belong to tested assemblies, not to boards. Code requirements are minimums from one model code and change with the edition and local amendments.
US gypsum board is made in standard thicknesses (½ in and ⅝ in are the most common); European plasterboard in 9.5, 12.5 and 15 mm. Type X and Type C contain fibres and additives that delay fire penetration, enabling rated assemblies. The rating is a property of the full tested assembly (board, framing, fasteners, insulation).
Classification: Stable (mature standard); codes change by edition
Gypsum board thicknesses and types have been stable for decades. Confirm the code edition your jurisdiction has adopted.
Thickness in inches and millimetres; weight in lb/ft² and kg/m²; fire rating in hours.
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