Roofing Area & Material Calculator

How the roofing area & material calculator works

Gross sloped area = length measured along the slope × rectangle width × number of identical planes. Deduct the entered area, which must not exceed gross area. This method does not convert pitch or horizontal plan dimensions to slope length.

Planning area = net area × (1 + ordering allowance / 100). Packs = ceil(planning area ÷ effective installed coverage per pack). Coverage must be positive and already account for the product’s installed exposure and laps. Material cost is whole packs × entered pack price, rounded half-up to cents.

Zero net area yields no packs or cost. Complex roofs need separately measured planes and appropriate cutting allowances. Starter, ridges, hips, valleys, flashing, fasteners, underlayment, labor and delivery are excluded. This is a coverage estimate, not roof-system selection, structural design or access advice. The roofing manufacturer’s document library provides product-specific estimating and installation context.

Worked example

Two identical rectangles measuring 5 m along the slope and 10 m along the eave total 100 m². With no deductions and a 10% allowance, planning area is 110 m². At 3 m² effective coverage per pack, 36.667 rounds to 37 packs. At an illustrative 25/pack, cost is 925. Changing slope length to 4 m requires 30 packs and 750.

Sources and assumptions

The source material explains the underlying calculation or pricing structure. Entered prices, costs, schedules and scenario choices are your assumptions; this tool does not obtain supplier quotes or predict actual results.

• Owens Corning roofing product and estimating documents