SettingsSettings for this calculationUS
The standard allowance most suppliers and estimating guides assume for ordinary work.
The area the roof covers, measured on plan.
This is the footprint, not the sloped surface — the area you would measure from above. The slope factor below converts it. Include the overhang beyond the walls, which is easy to forget and is several percent on a generous eave.
Rise in inches per 12 inches of horizontal run.
A 6:12 roof rises 6 inches for every 12 across. Measure it against a rafter or a batten rather than the covering, which sits proud. In metric terms 6:12 is a 26.6° pitch.
Cutting, starter courses, hips and valleys.
10% on a simple gable. 15% or more where there are hips, valleys, dormers or a complex plan — every valley is a diagonal cut on both sides and generates real offcut.
Roofing squares
15.86 squares
Geometry is exact for a plane roof. Hips, valleys and dormers add area beyond the plan projection, which the waste factor is there to absorb.
- Slope factor
- 1.12 ×
- True sloped area
- 1,442.26 sq ft
- With waste
- 1,586.49 sq ft
- Sloped area in sq ft
- 1,586.49 sq ft
- Pitch angle
- 26.57 °
They open the calculator with your figures already in it
Roof Squares Calculator: 15.86 squares — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
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How this was calculated
Formula source(s)
- 1 roofing square = 100 sq ft (9.2903 m²) of roof surface — universal North American roofing trade unit
- Slope factor = √(1 + (rise/run)²); the multiplier from plan area to true sloped area
Inputs used
- Roof plan area (footprint)
- 1290 sq ft
- Pitch — rise per 12 of run
- 6
- Waste (%)
- 10
Intermediate steps
- Slope factor
- 1.12 ×
- True sloped area
- 1,442.26 sq ft
- With waste
- 1,586.49 sq ft
- Sloped area in sq ft
- 1,586.49 sq ft
- Pitch angle
- 26.57 °
Confidence note: Geometry is exact for a plane roof. Hips, valleys and dormers add area beyond the plan projection, which the waste factor is there to absorb.
What this calculation does not cover
- One slope factor is derived from the single pitch figure and applied across the entire footprint, so a gambrel, a mansard or a lower-pitched extension roof has to be run as separate calculations and the square counts added together.
- Pitch is read as rise per 12 of run whatever measurement system the area is entered in, and the field stops at 24 in (610 mm) 12 — an angle in degrees or a percentage grade has to be converted to that form before it is typed in.
- Nothing is subtracted from the footprint you enter, so a chimney stack, a large rooflight or an open stairwell well is still counted as covered surface and should be taken out of the plan area first if it is big enough to matter.
- Waste is applied as a flat percentage of the finished surface, which spreads the cost of starter courses and cap shingles evenly over the field rather than counting the ridge and hip lengths that actually generate them; a small roof with a lot of edge needs a higher figure than the same percentage on a large plain one.
- The answer is left as a fractional square rather than rounded up, and no particular product sits behind it — bundles, rolls and sheets each cover their own share of a square, so turning this figure into an order quantity is a second step.
Estimated cost — your price
This site holds no price list for this material — local prices vary too much to publish honestly. Enter your supplier's price and the result is costed with it.
Part of bigger jobs
This trade is one line of several job takeoffs. Run the whole job and every other trade comes back with it, off the same measurements.
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Computed in your browser — nothing you enter is uploaded. Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.
Sources checked 2026-09-05 · in the site-wide review of 2026-09-06 · v1.0.1
Regulatory standards & verification citations2
- 1 roofing square = 100 sq ft (9.2903 m²) of roof surface — universal North American roofing trade unit
- Slope factor = √(1 + (rise/run)²); the multiplier from plan area to true sloped area
Cite this page
Your workspace
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Tools and safety for this job
To lay shingles. Generic types, no brands, no prices.
Protection this work requires
- Most fatal falls on small jobs are from under three metres: use a tower or a ladder tied at the top, and never work off the top two rungs.
- Knives cause more site injuries than any power tool: cut away from your body, change blades often, and wear cut-resistant gloves to EN 388 level C for repeated cutting.
Lay shingles: Roof work is the commonest cause of serious fall injury on domestic sites. Edge protection or a properly erected tower is the equipment that matters most here, and a roof that is steep, high, brittle or wet is a job for a roofer with the right access, not a longer ladder.
Show the 6 tools this job needsHide tools
Essential
Chalk line
Claw hammer
Extension ladder
Tape measure
Tower scaffold or trestles
Utility knife
Also needed as materials: chalk refill, replacement blades.
what each roofing tool is for, and the spec that decides which to buy where one does.