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Roof Shingle Calculator

Estimates asphalt shingles from the roof's horizontal footprint area and pitch: the pitch factor √(1 + (rise/12)²) converts the footprint to sloped surface area, which is expressed in roofing squares (100 ft²), increased by a waste allowance and converted to bundles and underlayment rolls. Planning estimate only.

Roof footprint area (ft² or m²)Horizontal (plan) area covered by the roof including eave overhangs, in ft² or m² (see area_unit); for a simple gable roof this is the building length × width plus overhangs. Area unit (optional)Unit of the area input; areas are reported in both m² and ft². Pitch (rise per 12) (optional)Roof pitch as rise per 12 units of run (6 means 6:12); ignored when pitch_degrees is given. Pitch (degrees) (°) (optional)Roof angle from horizontal in degrees; overrides pitch_rise_per_12 when given. Waste allowance (%) (optional)Extra material for cuts, breakage and offcuts, applied as a multiplier (1 + waste_percent/100). 10 % for simple gable roofs; 15 % for hip roofs, dormers and valleys. Bundles per square (optional)Bundles that cover one square (100 ft²): 3 for three-tab and most laminated (architectural) shingles, 4–5 for heavy designer shingles; printed on the bundle. Underlayment coverage per roll (ft²) (optional)Net coverage of one roll of underlayment in ft²: about 400 ft² (4 squares) for a #15 felt roll and for 4-square synthetic rolls, 200 ft² (2 squares) for #30 felt, 1,000 ft² (10 squares) for many synthetic rolls.

When to use

You need the number of shingle bundles, squares or underlayment rolls to order for a pitched roof whose plan area and pitch (x:12 or degrees) are known.

Do not use when: You only need to convert the pitch or find a rafter length (use roof-pitch), or the roof is metal, tile or membrane sold by the sheet (divide roof_surface_area_ft2 by the panel coverage instead).

Formula

pitch_factor = √(1 + (pitch_rise_per_12 / 12)²) (or 1 / cos(pitch_degrees)); roof_surface_area = roof_footprint_area × pitch_factor; squares = area_ft² / 100; squares_with_waste = squares × (1 + waste_percent/100); bundles = ceil(squares_with_waste × bundles_per_square); underlayment_rolls = ceil(squares_with_waste × 100 / underlayment_coverage_ft2_per_roll).

The footprint is measured in plan, so the pitch factor (the rafter multiplier of roof-pitch) recovers the true sloped area of every plane at that pitch; starter strips, hip and ridge caps, drip edge, flashing and nails are not included. Planning estimate only; check quantities against the supplier's coverage figures and local code before ordering.

Inputs

Parameter	Type	Unit	Required	Description
`roof_footprint_area`	number	ft² or m²	yes	Horizontal (plan) area covered by the roof including eave overhangs, in ft² or m² (see area_unit); for a simple gable roof this is the building length × width plus overhangs. Range: > 0, ≤ 1000000
`area_unit`	enum: m2 \| ft2		default ft2	Unit of the area input; areas are reported in both m² and ft².
`pitch_rise_per_12`	number		default 6	Roof pitch as rise per 12 units of run (6 means 6:12); ignored when pitch_degrees is given. Range: ≥ 0, ≤ 24
`pitch_degrees`	number	°	no	Roof angle from horizontal in degrees; overrides pitch_rise_per_12 when given. Range: ≥ 0, ≤ 85
`waste_percent`	number	%	default 10	Extra material for cuts, breakage and offcuts, applied as a multiplier (1 + waste_percent/100). 10 % for simple gable roofs; 15 % for hip roofs, dormers and valleys. Range: ≥ 0, ≤ 50
`bundles_per_square`	number		default 3	Bundles that cover one square (100 ft²): 3 for three-tab and most laminated (architectural) shingles, 4–5 for heavy designer shingles; printed on the bundle. Range: > 0, ≤ 10
`underlayment_coverage_ft2_per_roll`	number	ft²	default 400	Net coverage of one roll of underlayment in ft²: about 400 ft² (4 squares) for a #15 felt roll and for 4-square synthetic rolls, 200 ft² (2 squares) for #30 felt, 1,000 ft² (10 squares) for many synthetic rolls. Range: > 0, ≤ 5000

Outputs

Output	Type	Unit	Description
`pitch_factor`	number		√(1 + (rise/12)²) = 1 / cos(roof angle): sloped area per unit of plan area.
`roof_angle_degrees`	number	°	atan(rise / 12).
`roof_surface_area_ft2`	number	ft²	Footprint area × pitch_factor.
`roof_surface_area_m2`	number	m²	Same sloped area in square metres.
`squares`	number		roof_surface_area_ft2 / 100 (1 square = 100 ft² = 9.29 m²).
`squares_with_waste`	number		squares × (1 + waste_percent/100).
`bundles`	integer		ceil(squares_with_waste × bundles_per_square).
`underlayment_rolls`	integer		ceil(squares_with_waste × 100 / underlayment_coverage_ft2_per_roll).
`ridge_cap_note`	string		Reminder that hip and ridge cap shingles are estimated separately by linear length.

Example

1,500 ft² footprint, 6:12 pitch, 10 % waste, 3 bundles per square, 400 ft² rolls: {"roof_footprint_area":1500,"area_unit":"ft2","pitch_rise_per_12":6,"waste_percent":10,"bundles_per_square":3,"underlayment_coverage_ft2_per_roll":400} → {"pitch_factor":1.118,"roof_angle_degrees":26.57,"roof_surface_area_ft2":1677.1,"roof_surface_area_m2":155.8,"squares":16.77,"squares_with_waste":18.45,"bundles":56,"underlayment_rolls":5}

140 m² footprint, 30° pitch, 15 % waste, 1,000 ft² synthetic rolls: {"roof_footprint_area":140,"area_unit":"m2","pitch_degrees":30,"waste_percent":15,"underlayment_coverage_ft2_per_roll":1000} → {"pitch_factor":1.1547,"roof_surface_area_m2":161.66,"roof_surface_area_ft2":1740.1,"squares":17.4,"squares_with_waste":20.01,"bundles":61,"underlayment_rolls":3}

GET https://tttkmbb.com/api/v1/calculate/roof-shingles?roof_footprint_area=1500&area_unit=ft2&pitch_rise_per_12=6&waste_percent=10&bundles_per_square=3&underlayment_coverage_ft2_per_roll=400

Machine access

API: GET https://tttkmbb.com/api/v1/calculate/roof-shingles (query parameters) or POST with a JSON body {"inputs": {...}}
Schema: https://tttkmbb.com/api/v1/calculators/roof-shingles · Markdown: https://tttkmbb.com/construction/roof-shingles.md · JSON definition: https://tttkmbb.com/construction/roof-shingles.json
MCP: server https://tttkmbb.com/mcp, tool run_calculator with calculator_id="roof-shingles"
OpenAPI operationId: estimate_roof_shingles
Freshness: static. Authentication: none. Rate limit: fair use (see rate limits).

Sources

FAQ

Do I measure the footprint or the sloped roof?

Enter the horizontal footprint (building plan plus overhangs); the pitch factor converts it to sloped area. If you already measured the sloped area, enter it with pitch_rise_per_12 = 0.

How many bundles are in a square?

Three bundles per square is standard for three-tab and most laminated shingles (about 33 ft² per bundle); heavier designer shingles need 4–5, so check the bundle label.

Why does the roll count use the waste figure?

Underlayment is lapped 2–4 in horizontally and 6 in at end joints and is cut at hips and valleys, so the waste-inclusive area keeps the roll count conservative.

Related calculators

Roof Pitch Calculator — Convert the pitch and get the rafter multiplier.
Right Triangle Calculator — Sloped length of a roof plane from rise and run.