Construction material calculator

Result

Roof area (on the slope)

80 m²

Rows of sheets per slope

Sheets per row

Sheets to buy, with waste

Ridge caps, flashings, fixings and purlins are extra. The manufacturer's data sheet gives the cover width, the minimum pitch and the lap.

No cost is estimated: the site has no verified material price observations yet, and it does not estimate a cost from an unverified figure.

What this is for

How many roofing sheets cover a pitched or lean-to roof. It is an estimate for ordering and checking, not a design or a bill of quantities for a contract.

How it works

Rows up each slope: the fewest sheets that, lapped at their ends, reach from the eaves to the ridge.
Sheets in a row = length along the ridge ÷ the effective cover width, rounded up.
Sheets to buy = rows × sheets per row × slopes × (1 + waste %), rounded up.

Assumptions

Each one is an input above. None of them is a legal or standard requirement.

Assumptions used in this calculation
Assumption	Value used	Where it comes from
Roof slopes	2	Your choice. 1 for a lean-to, 2 for a simple pitched roof.
Sheet length	3 m	Product size.
Effective cover width of a sheet	0.8 m	Product size. The width a sheet covers after its side lap, from the manufacturer; it is less than the sheet's full width.
End lap between sheets	0.15 m	Site rule of thumb. Steeper roofs can take a shorter lap; the manufacturer gives the minimum for the pitch.
Waste allowance	5 %	Site rule of thumb. Cutting at hips, valleys and verges, and damaged sheets.

Worked example

A 10 m roof with two 4 m slopes, in 3 m sheets covering 0.8 m each with 150 mm end laps: two rows per slope and 13 sheets per row, 52 sheets, or 55 with 5% waste.

Limitations

Ridge caps, flashings, fixings and purlins are not included.
Hips and valleys waste more than a simple roof.
Quantities only: no labour, transport or cost.

Roofing sheets