Magply Board Thickness: 9mm, 12mm or 18mm?
Choosing the right Magply board thickness comes down to what the board is part of. We sell Magply in three thicknesses, 9mm, 12mm and 18mm, all as 2400 × 1200mm sheets. This guide compares them on weight, price and typical uses, so you know what to ask your designer or installer before you order.
Magply board thickness at a glance
| 9mm | 12mm | 18mm | |
|---|---|---|---|
| Sheet size | 2400 × 1200mm | 2400 × 1200mm | 2400 × 1200mm |
| Area per sheet | 2.88m² | 2.88m² | 2.88m² |
| Price per sheet (ex VAT) | £37.50 | £39.99 | £66.24 |
| Price per m² (ex VAT) | £13.02 | £13.89 | £23.00 |
| Weight per sheet (Magply brochure) | 28.5kg | Call us to confirm | 56kg |
| Product page | 9mm Magply | 12mm Magply | 18mm Magply |
The 18mm sheet costs about 1.7 times the 12mm sheet and weighs roughly twice as much as the 9mm one. The price jump from 12mm to 18mm is much bigger than from 9mm to 12mm, so it is worth knowing why you are choosing it. For the basics of the product, start with what Magply board is and what it is used for.
9mm Magply board
The 9mm Magply board is the lightest and lowest-priced sheet. Magply's published fire tests use 9mm board in several tested build-ups, including timber frame, load-bearing walls and a steel frame partition. Those results apply only to the exact constructions tested, so the thickness in your specification matters. It is often the choice where weight and cost matter and the design allows a thinner board.
12mm Magply board
The 12mm Magply board is the middle option. Magply's brochure shows 12mm board in tested spandrel panel and light gauge steel frame wall build-ups, and 12mm is the thickness our own 12mm Magply article focuses on. It adds stiffness over 9mm without the weight and cost of 18mm. The brochure lists a sound reduction figure of Rw 28dB for 9mm and Rw 29dB for 12mm, which is a very small difference, so do not choose a thickness for sound alone. These figures are for the board, not for a finished wall.
18mm Magply board
The 18mm Magply board is the heaviest and most expensive of the three, at 56kg a sheet. Choose it where your specification asks for 18mm, for example where the designer wants a thicker, more rigid board.
Can I use 18mm Magply as flooring?
This is a common question, and we want to give you a careful answer. Magply's literature describes thicker boards for structural roof and floor decks, and publishes separate guidance for them. We cannot confirm that the 18mm sheet we list is the same product as the certified structural deck, and we do not have joist spacings or load ratings for it. If you are thinking about a floor or roof deck, contact us on 03330 908479 or ask Magply's technical team before you order, and follow the manufacturer's instructions and your designer's specification. Never guess at joist centres for a structural floor.
Which thickness for which job?
| Job | What to do |
|---|---|
| Fire-rated wall or partition | Use the thickness, layers and fixings in the tested system. Do not swap them. |
| Timber or steel frame sheathing | Follow your designer’s specification, which sets the thickness |
| Internal wall lining where a mineral board is wanted | Ask your designer or installer, then see our guide to Magply vs plasterboard |
| Ceilings and loft spaces | Depends on the fire strategy and fixings, so check the system you are following |
| External walls, render or rainscreen | The whole system matters, so follow the system designer and Building Control |
| Floors and roof decks | Contact us or Magply first, see the section above |
How many sheets do I need?
Each sheet is 2.88m². For a 20m² wall that is 6.94 sheets, so 7 sheets with no allowance. Adding roughly 10% for cuts and offcuts, which is a rule of thumb rather than a figure from the manufacturer, gives 7.64, so 8 sheets. In 12mm that is 8 × £39.99 = £319.92 ex VAT. Note that this is below the £400 + VAT minimum order for free delivery shown on the product page, so you may want to combine it with other items from our building boards or insulation range.
Walls with many openings, or boards cut around awkward framing, will need more. Plan your layout first, then add the allowance.
Frequently asked questions
What thickness of Magply do I need?
It depends on the application and the specification. Fire tests, spandrel panels and framing systems each state a thickness, so follow the designer’s drawings or the manufacturer’s system. If you do not have a specification, call us or ask Magply’s technical team.
How heavy is a sheet of Magply board?
Magply’s brochure lists 28.5kg for a 2400 × 1200mm 9mm sheet and 56kg for an 18mm sheet. Call us for the 12mm figure. Plan a two-person lift.
Is 18mm Magply board suitable for flooring?
We cannot confirm that. Magply describes thicker boards for structural floors and roofs, but we do not have joist spacings or load ratings for the 18mm sheet we list. Contact us or Magply and follow the manufacturer’s instructions.
How do I cut and fix it?
Read our guide to how to fit Magply board, which covers score-and-snap cutting, fixings and dust safety.
Ordering and delivery
You can see all three sizes together in our Magply collection, or browse the wider range of building boards. Prices on our website are shown excluding VAT, and VAT is added at checkout. As stated on each Magply product page, we deliver free to addresses in England on orders of £400 + VAT or more. We cannot deliver to Wales, Scotland, Northern Ireland or the islands. Sheets arrive by Moffett lorry with a forklift offload, so someone must be there to receive them. We do not offer next-day delivery, so call us before you order if you have a date to hit. Our shipping policy has the full details. If you would like a hand choosing a board, call us on 03330 908479 or email sales@insulationwarehousedirect.co.uk.
This guide is general information, not a specification. Fire performance, fixings and suitability depend on the whole build-up and the project, so check them with your designer or Building Control and follow the manufacturer's instructions. Prices are correct at the time of writing (28 October 2026).