Corrugated Roofing Sheets Calculator

This calculator works out how many corrugated roofing sheets you need for a roof, based on the roof width and the sheet’s effective coverage width. Enter your roof width in metres and the sheet coverage width in millimetres, and it returns the number of sheets required, rounded up to the nearest whole sheet.

Formula

The number of sheets is calculated using the effective coverage width of each sheet, not the total sheet width. The formula is:

Sheets needed = ⌈ (Roof width in mm) ÷ (Effective coverage width in mm) ⌉

Where:

• Roof width (w) – the horizontal distance the sheets must cover, in metres.
• Effective coverage width (c) – the width of one sheet minus the overlap, in millimetres. This is the width that actually contributes to covering the roof.
• ⌈ ⌉ – the ceiling function, meaning you round up to the next whole number because you can’t buy a fraction of a sheet.

Worked Example

Using the default values: roof width = 10 m, sheet coverage width = 900 mm.

1. Convert roof width to millimetres: 10 m × 1000 = 10,000 mm.
2. Divide by coverage width: 10,000 ÷ 900 = 11.11.
3. Round up: 11.11 → 12 sheets.

So for a 10-metre-wide roof with sheets covering 900 mm each, you need 12 sheets.

Why Effective Coverage Matters

Corrugated sheets overlap at the sides to keep water out. The overlap means the physical sheet width is larger than the effective coverage. For example, a sheet might be 1 metre wide but have a 100 mm overlap, so its effective coverage is 900 mm. Using the physical width in calculations leads to underestimating the number of sheets.

Check the manufacturer’s data sheet for the effective coverage width – it’s often listed as “coverage” or “effective width.” If you only know the overall width and the overlap, subtract the overlap from the overall width.

How to Measure Your Roof Width

Measure the distance from the outer edge of the roof on one side to the outer edge on the other side, along the direction the sheets will run. This is usually the width of the building plus any eaves overhang. If the roof has multiple sections, measure each section separately and add the sheet counts.

For a gable roof, the sheets run from the ridge down to the eaves, so the width you need to cover is the horizontal span of the roof, not the slope length. The calculator assumes a single rectangular area; for complex roofs, break them into rectangles.

Common Mistakes

• Using overall width instead of coverage – the most common error; always use effective coverage.
• Forgetting to round up – even if you need 11.1 sheets, you must buy 12.
• Mixing units – if you enter roof width in feet and coverage in millimetres, the result will be wrong. Convert everything to the same unit first.
• Ignoring waste – this calculator gives the theoretical minimum. Add 5–10% for cutting, mistakes, and ridge or valley pieces.

Cost Considerations

Once you know the number of sheets, multiply by the price per sheet to get the material cost. Remember to include:

• Ridge caps, eaves fillers, and flashing.
• Fixing screws or nails – typically 6–8 per sheet.
• Underlayment or insulation if needed.
• Delivery charges and VAT if applicable.

Prices vary widely by material (galvanised steel, aluminium, polycarbonate) and thickness, so get a current quote from a supplier.

Safety and Installation Tips

• Wear gloves – cut edges of metal sheets are extremely sharp.
• Use a harness when working at height, and follow local safety regulations.
• Cut sheets with tin snips or a circular saw with a metal-cutting blade; avoid grinding, which can damage the coating.
• Install sheets from the bottom up, overlapping the upper sheets over the lower ones to shed water.
• Ensure the roof structure can support the weight of the sheets.

Frequently Asked Questions

What is the standard coverage width of corrugated sheets? Common coverage widths are 600 mm, 700 mm, 900 mm, and 1000 mm, depending on the profile and manufacturer. Always check the specific product.

How much overlap should I allow? Side overlaps are typically one corrugation (about 50–100 mm) for most profiles. End laps are usually 150–300 mm, but that doesn’t affect the number of sheets in a single row.

Can I use this calculator for polycarbonate sheets? Yes, the same formula applies – just use the effective coverage width of the polycarbonate sheet.

Do I need to add extra sheets for waste? Yes, it’s wise to add 5–10% to account for cutting, mistakes, and future repairs. For complex roofs, add more.

What if my roof width is not a multiple of the coverage width? You round up to the nearest whole sheet. The last sheet will be cut to fit, or you may need a narrower trim piece.

Does the roof slope affect the number of sheets? No, the number of sheets across the width is determined solely by the horizontal width and coverage width. However, the length of each sheet depends on the slope length, which is not covered by this calculator.

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in w | Roof width | m | 10 | 0
in c | Sheet coverage width | mm | 900 | 0
out n | Sheets needed | sheets | ceil(w * 1000 / c) | 0
out area | Roof area | m² | w * 1 | 2