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Sandwich Panel Quantity Calculator (Wall Coverage)

Calculate the number of sandwich/EPS/PUF panels needed for a wall by length, height, openings, panel size, and wastage allowance.

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Net Wall Area
26.00 m²
Panel Area
3.00 m²
Panels Required
10
Waste Area
4.00 m²

How this works

We compute the wall area to be covered, divide by the area of one panel, scale up by the wastage factor, and round up to the next whole panel:

netWallArea = wallLength × wallHeight − openingsArea
panelArea   = panelWidth × panelLength
nPanels     = ceil((netWallArea / panelArea) × (1 + wastagePct / 100))
wasteArea   = nPanels × panelArea − netWallArea

The covering invariant nPanels × panelArea ≥ netWallArea holds for any non-negative wastage, so the ordered panels always cover the wall.

Worked example

A 10 m × 3 m wall with 4 m² of openings, panels of 1 m × 3 m, and a 5% wastage allowance:

  • Net wall area = 30 − 4 = 26 m²
  • Panel area = 1 × 3 = 3 m²
  • Raw count = (26 / 3) × 1.05 ≈ 9.10
  • Round up = 10 panels
  • Waste area = 10 × 3 − 26 = 4 m²

Sources

  • Standard sandwich-panel coverage rule (gross − openings, ÷ panel area, × wastage)

FAQ

How is the number of panels computed?

We multiply wall length by wall height to get gross wall area, subtract the total area of openings (doors plus windows) to get net wall area, then divide by the area of a single panel and multiply by 1 + wastagePct/100. The result is rounded up to the next whole panel — you cannot order a fractional panel from the supplier. The covering invariant `nPanels × panelArea ≥ netWallArea` holds for any wastage ≥ 0.

What wastage percentage should I use?

5 percent is the conservative default for straight-run walls with minimal openings. Use 7 to 10 percent when the wall has many windows, irregular corners, or pitched-roof junctions that force diagonal cuts. For complex multi-level facades with stepped levels, 12 to 15 percent is realistic. Wastage covers cutting losses, breakage in transit, and replacements for site damage.

Should I treat each wall separately or sum all walls together?

If every wall uses the same panel size, you can sum the four wall lengths and the four window/door totals into a single calculation. If different walls use different panel sizes (for example, longer panels on the long side and shorter panels on the gable), run the calculator once per wall group and add the panel counts together — this gives a more accurate result than averaging.

Why does my answer round up instead of giving a decimal?

Sandwich panels are sold as whole units. Even if you only need 7.1 panels' worth of coverage, you must order 8 panels — the 0.9-panel offcut becomes part of the wastage allowance. The `wasteArea` field shows you exactly how much excess panel area you'll have on site, which is useful for planning offcuts into smaller wall segments or accessories.

What dimensions should I use for the panel width and length?

Use the supplier's nominal panel dimensions in metres. Korean panels are typically supplied as 1.0 m wide and made to length per order (commonly 2.5, 3.0, 4.0, or 6.0 m). EPS panels are sometimes 1.15 m or 1.20 m wide. Confirm the exact width with the supplier before ordering — a width difference of 50 mm changes the panel count noticeably on long walls.

Does this calculator handle openings of different sizes?

Yes — but only as a single sum. Add up the area of every door and window (in m²) and enter the total as `openingsArea`. For example, two 2.1 × 0.9 m doors and three 1.2 × 1.5 m windows give an opening area of (2 × 2.1 × 0.9) + (3 × 1.2 × 1.5) = 3.78 + 5.40 = 9.18 m².

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