Roofing Sheet Calculator
Work out how many profiled sheets, panels or tiles you need to cover a roof, allowing for side and end laps.
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Formula and method
The roof area is increased by the overlap percentage and the waste allowance, then divided by the usable area of one sheet. The result is rounded up to whole sheets.
Effective width, not nominal width
Profiled sheets overlap along one rib, so a sheet described as 1100 mm wide covers about 1060 mm once installed. The difference is 4 % per sheet, and over a 60 m² roof it is two or three extra sheets. The calculator uses the effective width, which is the number on the manufacturer's data sheet rather than the one in the product name.
Roof pitch changes the overlap too. A shallow roof needs a longer end lap to stop capillary action drawing water uphill, so the same panel covers less area at 10° than at 35°.
Overlap, fixings and the wind
End laps of 150 to 200 mm and side laps of one rib are normal, and both are included in the covering rate rather than being added afterwards. Fixings run at every second rib on the pans and at every rib on the edges, roughly 6 to 8 per square metre, and the edge fixings are the ones that fail first in a storm.
Screws with the wrong washer, overtightened or missing at the verge, are the most common cause of a leaking sheet roof. The sheet count is the easy part; the fixing schedule is what keeps it on the building.
Cuts, flashings and delivery
Hips, valleys and verge cuts produce offcuts that cannot be used elsewhere, and sheets are usually delivered at full length to avoid end laps. That means transport, access and lifting along the whole length of the panel, which for a 12 m sheet is a crane or a team of four.
Order the flashings, ridge and barge boards with the sheets. They come from the same supplier and the same colour batch, and a second order three weeks later rarely matches.
How to measure the inputs
- Work out the true roof area first, including overhangs.
- Measure the full sheet length and the usable width after the side lap.
- Confirm the overlap requirements for your profile and pitch from the datasheet.
Worked example
Roof area (optional) 1,076.39 ft²; Sheet length 13.12 ft; Sheet width 3.94 ft; Overlap 15 %; Waste 10 % → Roofing sheets: 32
Reference data
| Laying | Overlap, % | Useful width of a 1.15 m sheet |
|---|---|---|
| One wave | 8 | 1.06 |
| Two waves | 15 | 0.98 |
| Side and end lap | 12 | 1.01 |
Sheets overlap along the slope as well: 100 mm at up to 15°, 150 mm above that.
Practical tips
- Order a couple of spare sheets for later damage — profiles are discontinued.
- Check the manufacturer's minimum pitch for your chosen profile.
- Lift sheets with proper handling gear to avoid creasing thin profiles.
Sources
- ГОСТ 24045-2016 — Профили стальные листовые гнутые
Checked and updated October 22, 2026