Roof Area Calculator
A pitched roof’s real surface is larger than its footprint — the steeper it is, the more material it takes. Enter the plan size and pitch to get the true (sloped) roof area you actually buy tiles, sheets, underlay, waterproofing and insulation for — in m² and sq ft, with a wastage allowance.
Slope factor 1 / cos(22°) = 1.079 — the roof is 8% bigger than the footprint.
Allows for cuts, overlaps, ridges & hips. 5–10% for simple roofs, 10–20% for complex ones.
= 1,379 sq ft · incl. 10% wastage.
Indicative only — pick the row that matches your roof. Tile and sheet sizes vary by product; confirm coverage from the maker’s data.
A planning estimate. It treats the roof as a simple plane at the pitch you set, scaled by the slope factor 1 / cos(pitch). Real roofs have hips, valleys, dormers, overhangs and varying pitches, and material coverage differs by product — so take off actual quantities from the drawings before ordering. Structural design and any work at height are for a qualified engineer and roofing contractor.
Related Guides — Deep-dive reading
The Sloping Roof Design Guide
The roof that beats water by gravity — why a pitched roof suits Kerala, the Konkan and the hills, how to pick the pitch by material and rainfall, the truss-or-rafter structure, tiles vs metal sheet, and the underlay, battens, ridges, valleys, eaves and ventilation that make it last. Plain language, India-grounded.
RoofingDining Space Design in India: Where the Family Comes Together
Why a dining room can be too big, centring on the light, casual vs formal dining, table sizes and clearances, and the clever buffet-alcove trick
Room PlanningLiving Room Design in India: Built Around How You Actually Live
Resolving the three competing focal points, sizing to people not floor area, the double-height trap, and the formal-vs-family living room question
Room PlanningRelated Tools — You may also find these useful
Rainwater Harvesting Calculator
How much rainwater your rooftop can harvest in a year, in litres and kilolitres, from the roof area, your city's rainfall and roof type — with a suggested storage-tank size.
RoofingRoof Heat Gain Calculator
How much heat your roof lets in and how much insulation cuts it — heat gain in watts and the AC tonnage it adds, from roof construction (U-value), area and temperature difference, versus a bare slab.
RoofingRoof Pitch Calculator
Convert a roof's pitch between degrees, the rise-in-12 ratio (like 4:12), percentage grade and the slope (area) factor — or work the pitch out from rise and run.
Roofing