Plan area is not roof area
A pitched roof has more surface area than its horizontal footprint. Calculate the sloping length from rise/run or pitch, then use the true roof-face dimensions.
Roof covering units
Tiles, slates and shingles are ordered from effective coverage, not simply physical face dimensions. Headlap and sidelap reduce coverage, so use manufacturer figures.
Waste and cuts
Hips, valleys, verges, penetrations and complex geometry increase cuts and waste. Simple rectangular roofs usually waste less.
Underlay and battens
Membrane overlaps and batten gauge must be included. These are system-specific quantities and should be checked against the roof-covering specification.
Guttering
Measure eaves runs and account for outlets, corners, stop ends and stock lengths. Capacity and fall are separate design considerations.
Safety and region
BuildCalc supports the United Kingdom, United States, Canada, Australia, New Zealand, Ireland and South Africa. The geometry is universal, but terminology, units, pack sizes and common product dimensions differ. Use the dimensions printed on the product you intend to buy rather than assuming a regional default is exact.
Roof work is safety-critical. Quantity calculators do not determine structural adequacy, wind resistance, drainage capacity or safe working methods.
Use the related calculators
Use the calculator for your measurements, then return to this guide to check assumptions, allowances and ordering considerations.
Roof area & pitchRoof tiles / shinglesGuttering