Choose a roof geometry
Use measured surface, pitched run, or symmetrical gable mode for each section.
Roofing
Roofing Calculator
Estimate field-shingle roof area from measured roof surfaces, horizontal run plus pitch, or a symmetrical gable. Combine multiple roof sections, subtract optional surface-area exclusions, apply a user-selected allowance, and estimate whole shingle bundles from manufacturer coverage data.
Quantity estimator only.Use roof dimensions that include any eaves or overhangs that will receive shingles. This calculator does not design the roof, determine safe pitch, structural capacity, underlayment, flashing, starter strips, ridge or hip caps, ventilation, fasteners, snow or wind loads, code compliance, or safe roof access.
How to use the roofing calculator
Add each roof section using the measurement method that matches your information. Measured-surface mode uses dimensions taken along the roof plane. Pitched-run mode converts a horizontal run to sloped area from the entered rise-per-12 pitch. Symmetrical-gable mode uses the full horizontal span and already accounts for both equal roof planes.
Enter roof dimensions
Include eaves or overhangs that will receive shingles and repeat identical sections with quantity.
Apply your allowance
Add only the planning allowance appropriate for your roof, cuts, product, and project conditions.
Enter manufacturer packaging
Use coverage per bundle or bundles per roofing square, then optionally add price per bundle.
Roofing formulas
Measured roof surfaceArea = roof length × measured slope length
Pitch factorFactor = √(1 + (rise ÷ 12)²)
Pitched roof sectionArea = length × horizontal run × pitch factor
Symmetrical gableArea = roof length × total horizontal span × pitch factor
Net repeated sectionGroup area = (gross area − excluded surface area) × quantity
Roofing squaresRoofing squares = required ft² ÷ 100
Whole bundles from coverageBundles = ceiling(required area ÷ coverage per bundle)
Whole bundles from product packagingBundles = ceiling(required roofing squares × bundles per square)
Roofing example
A symmetrical gable that is 40 ft long, 24 ft across horizontally, and pitched 6:12 has about 1,073.313 ft² of roof surface. With a 10% allowance, the requirement becomes about 1,180.644 ft², or 11.806 roofing squares. If a test product requires 3 bundles per square, the project rounds to 36 whole bundles, providing 1,200 ft² of equivalent coverage and about 19.356 ft² above the calculated requirement.
Roofing calculator FAQs
What is a roofing square?
One roofing square is 100 square feet of roof area. The calculator reports decimal roofing squares rather than automatically rounding the area to a whole square.
Does symmetrical gable mode include both roof sides?
Yes. Enter the full horizontal span from eave to eave. The formula already accounts for both equal roof planes, so do not multiply the result by two again.
What does rise per 12 mean?
It is the vertical rise for every 12 units of horizontal run. A 6:12 pitch uses 6 as the rise value. The ratio is dimensionless, so the same pitch value works in Imperial and Metric mode.
Should I subtract skylights or chimneys?
You can enter an actual roof-surface exclusion for a section. Do not subtract an area equal to or larger than the gross section, and remember that small penetrations may not reduce purchasing by their theoretical area because cuts can create waste.
Does the calculator assume three bundles per square?
No. Bundle packaging varies by product. Enter the actual manufacturer coverage per bundle or bundles-per-square value.
Are ridge caps and starter shingles included?
No. Field shingles, ridge or hip caps, starter strips, underlayment, flashing, drip edge, ventilation, and fasteners can have different coverage and installation rules.
Can I use Metric measurements?
Yes. Linear dimensions switch between feet and meters, while exclusions and bundle coverage switch between square feet and square meters.
Does the calculator decide what roof pitch is safe?
No. Pitch suitability, product requirements, structural loads, code rules, and safe roof access are outside this quantity tool.
Can I save or share a roofing estimate?
Yes. After a successful calculation, the project state is stored in the URL when it fits within a conservative URL-size limit.
Reference methodology
The roof-pitch multiplier is calculated directly from right-triangle geometry rather than a rounded lookup table. Unit conversion uses the international foot relationship of exactly 0.3048 meter. Roofing squares are calculated as 100 ft² each. Bundle quantities require user-entered manufacturer packaging information and round only after the full project requirement has been combined.
Assumptions and limitations
- Measured-surface dimensions are actual dimensions along the roof plane.
- Pitched-run dimensions use horizontal run, not sloped length.
- Symmetrical-gable mode assumes two equal roof planes with the same pitch and uses the full horizontal span.
- Dimensions should include any overhang or eave area that will receive field shingles.
- Excluded area is entered as actual roof-surface area per repeated section and must not equal or exceed that section's gross area.
- The allowance percentage is user supplied and applied after exact net section areas are combined.
- Roofing squares are reported as decimal squares and are not automatically rounded to whole squares.
- Whole bundles are rounded only once at the final project level.
- Bundle coverage and bundles-per-square values must come from the actual product being purchased.
- Material cost includes only the entered bundle price and excludes labor, tax, delivery, tear-off, disposal, underlayment, flashing, accessories, and fees.
- This calculator does not estimate ridge-cap shingles, hip caps, starter strips, underlayment, ice barriers, flashing, drip edge, fasteners, ventilation, sheathing, framing, or structural loads.
- This tool estimates quantity only and does not determine product suitability, roof safety, or code compliance.