What size is a sheet of plywood, MDF or plasterboard?

Almost everything in British construction is built on a 1200mm module, which is why studs go at 400 or 600mm centres and why sheets are 1200 or 1220 wide. The 20mm discrepancy between the imperial-derived board sizes and the metric plasterboard sizes is a genuine trap and is worth knowing before you set out a stud wall.

Step by step

1. Learn the standard board sheet: 2440 by 1220.Plywood, MDF, chipboard, OSB, hardboard and most faced boards come as 2440 by 1220mm, which is exactly eight feet by four feet in old money. This is what "a sheet" means unless somebody says otherwise.
2. Learn the standard plasterboard sheet: 2400 by 1200.Plasterboard is metric, at 2400 by 1200mm, and also very commonly 1800 by 900mm, which is the size most people can actually carry. Some 2700 and 3000mm lengths are available for tall walls and for boarding in one piece to a ceiling.
3. Know about the European format: 2500 by 1250.Some imported board — particularly birch plywood and some MDF — comes as 2500 by 1250mm or 3050 by 1525mm. It is a genuine convenience for larger parts and a genuine nuisance if you are mixing it with 2440 stock.
4. Look out for half sheets and pre-cut panels.Most DIY sheds stock 1220 by 610 and 2440 by 610 panels, and various handy sizes. They cost more per square metre but they solve the transport and handling problem entirely, and for a small job they are often the cheaper total answer.
5. Set stud and joist spacings from the board you will actually use.Spacing at 400 or 600mm centres works for both formats because both divide by those numbers — but the last board in a run lands 20mm differently depending on which you are using. Set out from a real board, not from a nominal figure.
6. Do not mix 2440 board and 2400 plasterboard in one plane.If you are, for example, sheathing one part of a wall in OSB and boarding the rest in plasterboard, the edges will not coincide. Plan the layout so the different materials meet at a stud, not in the middle of a bay.
7. Check the actual sheet before you plan a tight layout.Manufacturing tolerance is small but real, and the factory edges are frequently not square or are damaged. If your cutting plan uses the full sheet, measure the sheet you have rather than the size on the label.

Tips

• Thicknesses are honest: an 18mm sheet really is 18mm, unlike solid timber's nominal sizing. Common thicknesses are 3, 6, 9, 12, 15, 18 and 25mm, with 12.5mm and 15mm for plasterboard.
• The 1220 width means a sheet spans exactly three stud bays at 400 centres or two at 600 centres, which is the whole reason those spacings exist.
• If you need a piece longer than 2440, ask about the larger formats before you plan a joint. A 3050mm birch ply sheet may save you a joint entirely.

Common mistakes

• Assuming plasterboard and plywood sheets are the same size — They are 40mm different in length and 20mm in width. In a layout where boards from both materials have to align, that discrepancy appears as an unsupported edge or a visible step.
• Designing a cutting list that uses the full 2440 by 1220 — The factory edges are often chipped, dented or out of square, and you should trim a few millimetres off all four sides before measuring. Leave that margin in the plan.
• Buying a full sheet for a job that needs 1200 by 600 — Two panels cost less than a sheet plus the transport, the handling and the cutting. Work out the pieces first.

Questions people ask