Roofing Calculator
Roof area, squares and every material to order, for shingles or metal sheets.
Roof
Roofing
Prices optional
Prices optional
Materials
| Item | Quantity | Based on | Cost |
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About the Roofing Calculator
Work out the true area of a pitched roof and what it takes to cover it. Enter the building footprint, the overhangs and the pitch of a gable, hip or shed roof; the calculator turns the plan area into sloped area with the pitch factor and gives squares, shingle bundles, underlayment rolls, ridge cap, starter, drip edge and nails — or, in sheet mode, the number and length of metal, GI or colour-coated roofing sheets, ridge pieces and screws.
Product figures such as bundles per square, roll coverage and a sheet’s cover width differ between makers, so every one of them is an input you can match to the wrapper or data sheet.
How to use it
- Pick Metric or US units and the roof type. Enter the building length and width (outside of the walls) and the overhangs at the eaves and gable ends.
- Enter the pitch as rise in 12, degrees or percent — or tap a common pitch. The roof area, rafter length and rise update as you type.
- Choose Shingles or Sheets. For shingles, check bundles per square, the underlayment roll and the ridge-cap coverage on the wrappers; for sheets, enter the cover width of the profile, whether sheets are cut to length or come in stock lengths, and the end lap.
- Add prices if you want a cost, then copy the list or download it as CSV.
Examples
Plan 42 × 32 = 1,344 sq ft × 1.118 = 1,502.6 sq ft = 15.03 squares → 17.28 with waste → 52 bundles (3 per square), 2 synthetic rolls, ridge 10 ft + 4 hips of 24 ft = 106 ft → 5 ridge-cap bundles (25 ft each), 148 ft of drip edge = 15 pieces, 5,530 nails
Plan 10.6 × 9 = 95.4 m² × 1.118 = 106.66 m² (11.48 squares); rafter 5.03 m; ridge 2 m above the walls
10.6 m ÷ 1.0 m = 11 sheets per slope × 2 slopes = 22 sheets of 5.03 m; + 5% = 24 sheets = 120.7 m running length; ridge in 2.5 m pieces lapped 150 mm = 5 pieces
2 sheets along each slope → 44 sheets; + 5% = 47 sheets
How the roof area is worked out
Plan area = (length + overhangs) × (width + overhangs). Every plane of a gable, hip or shed roof here has the same pitch, so sloped area = plan area × pitch factor √(1 + (rise ÷ run)²) — 1.054 for 4 in 12, 1.118 for 6 in 12, 1.202 for 8 in 12 and 1.414 for 12 in 12.
On a hip roof with equal pitches the ridge is length − width and each of the four hips is (width ÷ 2) × √(2 + (rise ÷ run)²), all measured to the outside of the overhangs. A square is 100 sq ft (9.29 m²) of roof.
What each material is based on
- Bundles = squares × (1 + waste) × bundles per square. The wrapper says how many bundles make a square; many shingles are packed three to the square, heavier ones four or five.
- Underlayment = roof area × (1 + waste) ÷ the roll’s net coverage (after its laps).
- Ridge cap covers the ridge and all hips; starter runs along the eaves (and the rakes if ticked); drip edge goes along the eaves and rakes — and the high edge of a shed roof.
- Nails = shingles × nails per shingle, where shingles per square = 100 sq ft ÷ (shingle length × exposure): 80 for 36 in shingles laid 5 in to the weather, 65 for metric shingles at 5⅝ in. Use the number of nails the wrapper asks for (more in high-wind areas).
- Sheets = ⌈(roof length incl. gable overhangs) ÷ cover width⌉ per slope × sheets along the slope, where sheets along the slope = ⌈(rafter − end lap) ÷ (sheet length − end lap)⌉.
Waste allowance
The starting allowances are 10% for gable and shed roofs and 15% for hip roofs, which have many more cut shingles along the hips. They are rules of thumb: add more for dormers, valleys, skylights and complicated roofs, and check with your roofer.
Limitations
- Roofs with valleys, dormers, different pitches or L-shaped plans are not one of these shapes: work out each section separately and add them up.
- Hip roofs in sheet mode would need sheets cut to triangles along every hip, so sheet mode covers gable and shed roofs only.
- Ice-and-water shield, valley flashing, vents and fixings other than nails and sheet screws are not counted.
- Follow the shingle or sheet maker’s minimum pitch and fixing instructions; this is a quantity estimate, not a design.
Privacy
Everything happens in your browser. What you enter or open here is not uploaded or stored by MySmartCoPilot.
Frequently asked questions
How do I find the area of my roof from the ground?
Measure the outside of the building (length and width), add the overhangs at the eaves and gable ends, multiply to get the plan area, then multiply by the pitch factor for your slope. A 6 in 12 roof is 1.118 times its plan area.
How many bundles of shingles are in a square?
It depends on the product — the wrapper says. Many standard and architectural shingles are packed three bundles to a square (100 sq ft); some heavy designer shingles take four or five.
What does 6/12 pitch mean?
The roof rises 6 inches for every 12 inches it runs horizontally — a slope of 0.5, or about 26.6°. Type the pitch in degrees or percent if that is how you measured it.
How many roofing sheets do I need?
Divide the length of the roof (with the gable overhangs) by the sheet’s cover width — the width each sheet adds after the side overlap — and round up; that is the sheets per slope. If the slope is longer than one sheet, multiply by the sheets needed along the slope with their end laps.
Why is a hip roof’s waste higher?
Each hip needs shingles cut at an angle on both sides, and the triangular ends have more cut pieces, so more material is wasted than on a plain gable.