Roofing Sheet Calculator
Home & ConstructionSheets, screws and ridge for a pitched roof, allowing for the slope and the side lap.
Runs entirely in your browser — nothing is uploaded
Roofing orders come up short for two reasons, and both are geometry. A pitched roof is larger than the plan it is drawn on — a 1-in-4 slope is 3% more material, a 1-in-2 slope is 12% more. And a sheet covers less than its manufactured width once the side lap is taken up. This accounts for both, then adds the end laps, the overhang and the fixings.
What people do next
Features
- Plan dimensions converted to true sloping area for any pitch.
- Five common profiles, each with its real effective cover and end lap.
- Gable or lean-to, with the eaves overhang included.
- Sheets across and courses up the slope, shown separately.
- Screws, ridge cap and gutter lengths estimated.
- Calculated in your browser — nothing is uploaded.
How to use the Roofing Sheet Calculator
- 1Enter the plan length and width of the building.
- 2Choose the roof shape and the pitch.
- 3Pick the sheet profile and the length you can get.
- 4Read the sheet count, the fixings and the accessories.
Frequently asked questions
How do I work out roof area from the plan area?
Multiply by the slope factor, which is √(1 + (rise ÷ run)²). A 1-in-4 pitch gives 1.031, so the roof is 3.1% larger than its footprint; a 1-in-2 pitch gives 1.118, or 11.8% larger. Then add the eaves overhang on every side. Ordering on the plan area is the most common reason a roof finishes short.
Why does a sheet cover less than its width?
Because the sheets overlap along their edges to keep water out — usually one or two corrugations. A 1,000 mm GI corrugated sheet covers about 850 mm once laid, and a 1,220 mm trapezoidal sheet covers about 1,070 mm. Dividing the roof length by the manufactured width rather than the effective cover leaves you a sheet short of the far edge.
How much should sheets overlap at the ends?
150–200 mm for a normal pitch, more on a shallow one where water runs off slowly and wind can drive it back up the lap. The flatter the roof, the more the lap matters. A single sheet running from eave to ridge needs no end lap at all, which is why longer sheets waste less material even though they are harder to handle.
How many screws does a roofing sheet need?
About 5–6 self-drilling screws with EPDM washers per square metre, depending on the profile and the purlin spacing. Fix at the crown of the corrugation, never in the valley — a screw in the valley sits in the path of the water and the roof will leak at every one of them.
What pitch does a metal roof need?
At least 1 in 12 for most profiles, and more where rainfall is heavy or the sheets are short. Below that, water moves too slowly, capillary action pulls it back through the laps, and debris collects. Manufacturers publish a minimum pitch for each profile — check it before settling on a shallow roof for the look of it.