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Foil-faced PIR insulation board, one of the products priced by Insulation Warehouse Direct's free calculators

Free Insulation, Plasterboard and Ceiling Calculators (UK)

By , Managing Director

Planning a loft, a PIR floor or wall, a plasterboard room, an MF ceiling, a 600×600 suspended ceiling or a metal stud partition? Use the free calculators on Insulation Warehouse Direct. Enter your sizes, get a materials list priced live from the shelves, and add it to your basket. Then tweak quantities if you need to.

Results are estimates, to help you order the right amount first time. Check the final specification with your installer, Building Control or the manufacturer. Questions? Call 03330 908479.

Why we built them

Thickness guides are easy to find. A calculator that uses the products we actually sell, rounds up to whole packs and gives you a priced list is much harder to find. We looked at the other UK insulation merchants and could not find another shop offering this set — especially the MF ceiling, suspended ceiling, partition and PIR U-value tools.

Manufacturer U-value tools (Kingspan, SOPREMA / Celotex, Knauf Insulation, ROCKWOOL and others) are excellent for a detailed build-up. Ours is different: it is a quick Part L check that then prices the boards we stock, so you can order.

The calculators

Start at the calculators hub, or jump to the one you need.

PIR U-value calculator

Open the PIR U-value calculator

What it does: Find the PIR thickness you need for a floor, wall or roof to meet Approved Document L U-value targets, then price the boards we stock.

How to use it:

  1. Pick the element (solid floor, beam and block, timber floor, cavity wall, timber frame, internal wall, pitched roof or flat roof).
  2. Enter the details it asks for (for a floor, that includes the perimeter-to-area ratio).
  3. Check the U-value against the Part L target and see the thinnest board that meets it.
  4. Enter the area if you want a pack count and a price, then add the boards to your basket.

Treat this as a guide, not a certified calculation. Always confirm with Building Control or the manufacturer’s own U-value tool if the job needs it.

Insulation calculator

Open the insulation calculator

What it does: Turns an area into packs of PIR boards, mineral wool rolls or slabs, with a waste allowance, priced live.

How to use it:

  1. Choose where the insulation is going.
  2. Enter the area in m², the number of layers and a waste percentage (10% is a sensible start).
  3. Pick the product and thickness. Coverage comes from the pack or sheet size, not a guess.
  4. Add the packs to your basket. Work out each area separately if you have more than one.

Loft roll calculator

Open the loft roll calculator

What it does: Loft floor area to whole rolls of ODE, Knauf Insulation or URSA loft roll, with layers and waste, priced live.

How to use it:

  1. Measure the loft floor and enter the area in m².
  2. Pick the roll and thickness. Coverage is the m² printed in the product name (for example, a Knauf Loft Roll 44 Combi-Cut 200mm roll covers 6.84m²).
  3. Set the number of layers. For two different thicknesses (typically one between the joists and one across them), run the calculator once for each layer.
  4. Keep waste at 10% unless the loft is cut up by tanks, chimneys or trusses.
  5. Add the rolls to your basket.

Current UK guidance for a loft insulated at the joists is around 270mm of mineral wool in total. Check what your Building Control body needs if it is part of building work.

Plasterboard and fixings calculator

Open the plasterboard calculator

What it does: Room size to boards, drywall screws, dot-and-dab adhesive, tape and filler or skim plaster, priced live.

How to use it:

  1. Enter the room length, width and height, and tick walls and/or ceiling.
  2. Add doors and other openings.
  3. Choose the board, how it is fixed, and the finish (tape and joint or skim).
  4. Check the list and press Add all to basket.

Screws, adhesive and plaster quantities follow published British Gypsum and compound coverage figures. Uneven walls use more adhesive.

Access panel size guide

Open the access panel size guide

What it does: Enter the opening you need, pick a fire rating and finish, and see the FlipFix panels that fit, priced live.

How to use it:

  1. Measure the opening you need to get to the service (valve, fan, junction box or ceiling void).
  2. Choose non fire rated, 1 hour or 2 hour, and a metal or plasterboard face.
  3. The guide lists panels that are at least that size, smallest first.
  4. Add the panel to your basket.

If the wall or ceiling is fire-rated, the panel should carry a matching rating.

Suspended ceiling calculator

Open the suspended ceiling calculator

What it does: Sets out a 600×600 (or 1200×600) grid for your room and lists main tees, cross tees, wall angle, hangers and tiles, priced live.

How to use it:

  1. Measure the room wall to wall and enter the length and width.
  2. Enter the drop from the soffit if you need hanger wire.
  3. Pick the tile and grid. The drawing centres the grid so cut borders are equal and not less than half a tile.
  4. Tap any tiles you want to leave out for lights or obstructions.
  5. Press Add whole kit to basket, or email the list for a quote.

Only know the m²? Enter 1 × your area (for example 1 × 500). Very large areas are worked out from a trade rule of thumb, with a little spare built in.

MF ceiling calculator

Open the MF ceiling calculator

What it does: Works out MF7 primary channels, MF5 furring sections, MF6A perimeter, hangers, clips, plasterboard and screws for a suspended plasterboard ceiling, from British Gypsum GypCeiling MF guidance.

How to use it:

  1. Enter the room length and width, and the drop from the soffit.
  2. Choose MF5 centres (450mm is the usual maximum for 12.5mm and 15mm board; 400mm if you want every end of a 2400mm board to land on a section).
  3. Pick the plasterboard and metal range.
  4. Check the list and press Add all to basket. Metal is sold in packs of 10; the calculator rounds up and shows the price per length.

This is a guide for a simple rectangular room. Fire or acoustic specifications, lights and access panels can change the list — call us and we will check it.

Drywall partition calculator

Open the partition calculator

What it does: Works out studs and track, door openings, boards, screws and acoustic roll for a metal stud partition, following British Gypsum metal stud guidance.

How to use it:

  1. Enter the wall length and height, and the stud centres (often 600mm; 400mm where the specification asks for it).
  2. Add door openings if you have them.
  3. Choose the stud width, boards (one side or both, one layer or two) and whether you want acoustic roll in the cavity.
  4. Press Add to basket. You can change quantities in the basket.

50mm or 70mm studs suit most domestic walls up to about 3m. Go wider for taller walls, better sound insulation or services in the cavity, and check the system’s maximum height.

A few things to know before you order

  • Every list is an estimate. Awkward shapes, extra layers, fire ratings and site waste will change the quantities.
  • Insulation, plasterboard, ceilings and general building materials have a £400 ex VAT minimum order. We deliver to England, mainland Wales and mainland Scotland. Call 03330 908479 if you are unsure which rate applies to your basket.
  • Prices on the calculators are live from the shop, shown ex VAT, with VAT at 20% on the total.
  • You can change quantities in the basket after you add the list.

Need a second pair of eyes? Call 03330 908479 or email sales@insulationwarehousedirect.co.uk with your sizes and we will check the list.

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