Insulation calculator
Calculate insulation packs for ceilings, walls or floors.
Insulation calculator
Calculate how much insulation you need for ceiling, wall or floor based on dimensions, thickness and waste.
Surface length
Surface width (or height for walls)
Allowance for cutting and extra consumption
Check packaging — varies by product and thickness
Your insulation project
26.4 m² insulation (100 mm) → 8 packs for 24 m² ceiling
Area
24 m²
Thickness
100 mm
Incl. waste
26.4 m²
Packs
8
Materials
24 m² ceiling + waste
8 × 3.6 = 28.8 m² (surplus: 2.4 m²)
ℹThe result is an estimate based on dimensions, insulation thickness, pack coverage and waste.
ℹActual requirements may vary depending on construction, cutting and product choice.
Example: 24 m² ceiling
If you insulate a 24 m² ceiling with 100 mm insulation and add 10 % waste, you need about 26.4 m² of insulation. If a pack covers 3.6 m², you need 8 packs.
Calculation for a 6 × 4 metre ceiling:
The surplus from rounding is a natural part of the calculation — it provides a small reserve for mistakes and cutting.
How to calculate insulation
Always add waste
Insulation batts must be cut at edges, corners, pipes and electrical boxes. 10 % extra is a good starting point. With many penetrations or irregular shapes 15 % may be more realistic.
Thickness matters
Insulation performance (U-value) depends directly on thickness. Ceiling insulation typically needs 200+ mm to meet building regulations, while interior walls can manage with 45–95 mm. Always check the requirements for your project.
Pack coverage varies
Each pack of insulation covers a certain number of m² — typically between 2 and 6 m² depending on product and thickness. Thicker insulation yields fewer m² per pack. Always check the packaging before ordering.
Ceiling, wall and floor have different needs
Ceiling insulation is typically laid in 2 cross-laid layers to avoid thermal bridges. Walls are usually insulated in a single layer between studs. Floor insulation requires a vapour barrier and must fit the construction depth. The calculator handles all three types.
How to use this calculator
Four quick steps – you don't need to be a tradesperson to follow them.
- Measure the area you're insulating – ceiling, wall or floor.
- Choose the insulation thickness (e.g. 95 mm, 195 mm).
- Enter how many m² come per pack – it's on the label in the shop.
- Check the pack count and round up. Add about 5 % for waste around studs and pipes.
Common mistakes
Small things that often cost an extra trip to the hardware store.
- Underestimating the volume – packs are bigger than they look, but you must never compress insulation.
- Forgetting the vapour barrier – insulation alone won't help if moisture gets through.
- Wrong thickness – check what your local building regulations require.
- Not packing the gaps around studs, rafters and pipes properly.
Example: a 60 m² loft
A 60 m² loft with 195 mm mineral wool at 5 m² per pack is 12 packs by area. Add 5 % waste and you're at 13 packs. Don't forget the vapour barrier and tape on top.
Frequently asked questions
Short answers to the questions we hear most often about this calculator.
How thick should the insulation be?
It depends on whether it's a loft, wall or floor – and whether it's a new build or a retrofit. Lofts are often 300+ mm, walls 195–245 mm. Check your local building regulations.
Do I need a vapour barrier?
Yes, on the warm side – otherwise you risk moisture and mould inside the construction.
Does this work for both glass wool and rock wool?
Yes – it works off area and thickness, so the principle is the same either way.
How much waste should I plan for?
5 % is usually plenty. If you're filling around lots of close studs or pipework, push it to 10 %.
Use the results in a real project
With MyPlanDIY you can save materials, create budgets, track tasks and bring everything together in one project.
No credit card required. Free demo project included.
See also
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