Roofing calculator: area, squares and materials
This roofing calculator turns the building’s footprint and roof pitch into the true sloped roof area, then into the materials you order: asphalt shingle bundles, profiled metal sheets, clay or concrete tiles, and rolls of underlayment. It reports square metres and roofing squares (100 ft²), adds a waste percentage for cuts and gives a cost estimate in your currency.
The key number is the pitch factor: a roof that rises 6 in for every 12 in of run is 11.8% longer along the slope than the flat footprint, so a 1,200 ft² footprint becomes 1,342 ft² of roofing. Gable, hip, shed and flat roofs are all handled — a hip roof has the same surface area as a gable roof of the same pitch, but a shorter ridge and four hips to cap.
Enter the overhang at the eaves so the area covers the real roof edge, and use the ridge, hip and rafter lengths for cap shingles, ridge tiles and battens. To convert a pitch between x/12, degrees and percent, use the roof pitch calculator; for rafter cut lengths, birdsmouth and plumb cuts, the rafter calculator.
How to use the Roofing Calculator
- Choose metric or imperial, then enter the building length (along the ridge), width and the eave overhang per side.
- Pick the roof shape and the pitch — a standard rise-per-12 value, or a custom angle in degrees or rise per 12.
- Choose the covering: shingles (coverage per bundle), metal sheets (effective width and length), tiles (tiles per m² or ft²) or area only.
- Set the waste percentage and the coverage of one underlayment roll (0 to skip), then the price per bundle, sheet, tile or square.
- Read the roof area, squares, bundles or sheets, underlayment rolls and cost; copy or share the summary for quotes.
Roofing Calculator features
Pitch factor table built in
Choose 2/12 to 12/12, or type an angle; the factor √(1 + (rise/12)²) is shown with the angle.
Four roof shapes
Gable, hip, shed and flat, with ridge, hip and rafter lengths for caps and battens.
Shingles, sheets or tiles
Bundles at 3 per square, sheets counted across and up each slope, or tiles per square metre.
Underlayment rolls
Synthetic (10 squares) or felt (4 or 2 squares) rolls from the coverage you enter.
Waste and overhang
Eave overhang is added to the footprint; waste is added before rounding to whole bundles or sheets.
Both unit systems
Square metres and roofing squares side by side; inputs convert when you switch.
How the roof area is calculated
Metal sheets are counted differently: sheets across a slope = slope length along the ridge ÷ effective sheet width, sheets up a slope = rafter length ÷ sheet length, both rounded up, times the number of slopes, plus waste.
- Footprint = (length + 2 × overhang) × (width + 2 × overhang).
- Pitch factor = √(1 + (rise ÷ 12)²) = 1 ÷ cos(angle). For 6/12 it is 1.118; for 30° it is 1.155.
- Roof area = footprint × pitch factor. 40 × 30 ft = 1,200 ft² × 1.118 = 1,341.6 ft² = 13.4 squares.
- Order = roof area × (1 + waste). With 10%: 14.76 squares → 45 bundles of shingles (3 per square), 2 rolls of synthetic underlayment.
Roof pitch factor table
| Pitch (rise / 12) | Angle | Factor | Area of a 100 m² footprint |
|---|---|---|---|
| 2 / 12 | 9.5° | 1.014 | 101.4 m² |
| 3 / 12 | 14.0° | 1.031 | 103.1 m² |
| 4 / 12 | 18.4° | 1.054 | 105.4 m² |
| 5 / 12 | 22.6° | 1.083 | 108.3 m² |
| 6 / 12 | 26.6° | 1.118 | 111.8 m² |
| 7 / 12 | 30.3° | 1.158 | 115.8 m² |
| 8 / 12 | 33.7° | 1.202 | 120.2 m² |
| 9 / 12 | 36.9° | 1.250 | 125.0 m² |
| 10 / 12 | 39.8° | 1.302 | 130.2 m² |
| 12 / 12 | 45° | 1.414 | 141.4 m² |
Material notes
- Asphalt shingles: 3 bundles cover one square (33.3 ft² each); architectural shingles sometimes need 4. Ridge cap is sold separately — use the ridge and hip lengths.
- Metal sheets: use the effective cover width (after side laps), e.g. 1.0 m for a 1.06 m sheet, and round the sheet length up to the next stock length so laps are not needed up the slope.
- Tiles: Indian Mangalore tiles need around 15 per m², concrete interlocking tiles about 10 per m², flat clay tiles 50–60 per m². Enter the figure from the supplier.
- Sloped roofs collect rain — size a tank with the rainwater harvesting calculator — and the solar panel calculator shows how many panels the roof could hold.
Roofing Calculator FAQ
How do I calculate roofing squares?
Multiply the footprint by the pitch factor to get the sloped area in square feet and divide by 100. A 1,200 ft² footprint at 6/12 is 13.4 squares; add 10% waste and order 15 squares — the roofing calculator does this and converts to bundles.
How many bundles of shingles do I need per square?
Three bundles of standard three-tab or architectural shingles cover one square (100 ft²), so each bundle covers about 33.3 ft² (3.1 m²). Some heavier designer shingles need four.
Does a hip roof need more material than a gable?
The surface area is the same for the same footprint and pitch, but hips create more cut waste and need hip cap along four edges, so allow 15% waste rather than 10%.
What pitch factor should I use for 30 degrees?
1 ÷ cos(30°) = 1.155. Choose “Custom angle in degrees” and type 30; the calculator shows the factor and the equivalent 6.9/12 rise.
How much underlayment do I need?
The same area as the shingles, including waste. A synthetic roll covers about 10 squares (93 m²), #15 felt 4 squares, #30 felt 2 squares. Enter the roll coverage and the tool rounds up to whole rolls.
Is the cost estimate the full roofing price?
No. It prices only the covering you chose; underlayment, flashing, ridge cap, nails, battens, labour and tax are extra. Use it to compare materials and sanity-check quotes.