Insulation calculator

Work out how many boards, slabs or rolls you need. Pick where the insulation is going, enter the area and choose a product and thickness from our range. We use the coverage of each sheet, pack or roll exactly as we sell it, add a waste allowance, round up to whole packs and price it live, ex and inc VAT, so you can add it straight to your basket.

Not sure what thickness you need? Use the PIR U-value calculator first, then come back here for quantities.

Your job

Area
The area to be insulated, in square metres.
e.g. 2 for a loft topped up across the joists.
For cutting and offcuts. 10% suits most jobs.

Your insulation

View product Call 03330 908479

Estimate only. Quantities are based on the area you enter and the coverage of each sheet, pack or roll as sold. They don’t allow for the space taken by joists, studs or rafters, awkward shapes or extra layers you haven’t entered. Check the thickness you need for Building Regulations with your builder, building control or the manufacturer’s literature. Call us on 03330 908479 and we’ll happily check it before you order.

How to use the calculator

  1. Choose where the insulation is going: loft, pitched roof, flat roof, floor, cavity wall, solid wall or stud wall.
  2. Enter the area in square metres, or the length and width and we’ll work it out.
  3. Pick a product and thickness. Only products we can price and pack out online are listed.
  4. Set the number of layers and the waste allowance (10% to start with).
  5. Check the result and press Add to basket. Work out each area separately and add them one at a time.

How we calculate

  • Coverage comes straight from the product: a 2400 × 1200mm sheet covers 2.88m², a pack or roll covers the m² shown in its name (e.g. ‘Pack of 10, 5.4m²’ or ‘10.83m² roll’).
  • Area needed = your area × layers, plus the waste allowance.
  • Packs = area needed ÷ coverage per sheet, pack or roll, rounded up to whole units.
  • Prices are live from the shop, ex VAT, with VAT at 20% shown for the total.
  • Products whose coverage can’t be read from the product details are left out rather than guessed.

Questions

How much waste should I allow?

10% is a sensible starting point for boards and rolls in a simple rectangular area. Allow more for lots of cutting round joists, rafters, windows or services, and less for large open areas.

Do I deduct the joists or studs?

No, this calculator uses the full area. Rolls and slabs fitted between joists or studs are usually cut from the full width, and the offcuts help cover the ends, so the full area plus waste is a reasonable estimate.

How thick should my insulation be?

It depends on the element and the U-value you need to achieve. Our PIR U-value calculator gives a guide for PIR boards, and your building control body or designer can confirm what’s needed for your project.

Is there a minimum order?

Yes. Insulation and building materials have a £400 ex VAT minimum order. Delivery is free to England & Wales on orders over £500 ex VAT and £50 ex VAT below that.

Can you check my list?

Of course. Call us on 03330 908479 or email sales@insulationwarehousedirect.co.uk with your sizes and we’ll check the quantities and suggest alternatives if something’s out of stock.