Roofing Calculator Guide
A roofing calculator estimates roof area, shingle squares, underlayment, and material costs. Enter footprint dimensions, roof pitch, and overhangs to get a complete takeoff with a sensible waste factor.
What is Roofing Calculator?
The roofing calculator handles rectangles, L-shapes, and individual planes. It converts roof pitch into a slope factor to adjust plan area into true roof surface area and summarizes materials by the square.
How to Use the Roofing Calculator
- Enter building footprint (length x width) and overhangs.
- Select pitch (rise over 12). The tool applies a pitch factor.
- Add planes for complex roofs and sum areas.
- Choose waste (10-15% typical; more if highly cut-up).
- Calculate squares, bundles, underlayment rolls, and cost estimate.
Formulas & Methods
- Plan area:
A_plan = L*W(add for each section). Include overhangs. - Pitch factor:
factor = sqrt(1 + (rise/run)^2)withrun=12. Examples:4/12 -> ~1.054,6/12 -> ~1.118,8/12 -> ~1.202. - Roof area:
A_roof = A_plan * factor. - Squares:
Squares = A_roof / 100. Bundles ~= Squares * 3(typical 3-tab). - Waste:
A_total = A_roof * (1 + waste%). Add starter, hip, ridge as separate line items if desired.
Assumptions & limitations
- Factors assume straight gable planes; hips/valleys add complexity and waste.
- Local code may require ice & water shield at eaves/valleys; add separately.
- Steep-slope safety and access may change labor and waste.
Examples
Example A — 40x30 ft, 6/12 pitch
A_plan = 1,200 sq ft. Factor 1.118 -> A_roof ~ 1,342 sq ft.
Waste 12% -> A_total ~ 1,503 sq ft.
Squares = 15.0; Bundles ~ 45.
Example B — Two rectangles
32x24 ft plus 20x12 ft, pitch 8/12.
Plan = 768 + 240 = 1,008 sq ft. Factor 1.202 -> 1,211 sq ft.
Waste 10% -> 1,332 sq ft -> 13.3 squares.
| Item | Quantity | |---|---:| | Shingles (bundles) | ~45 | | Underlayment (10 sq/roll) | ~5 rolls | | Drip edge | perimeter length | | Nails | per manufacturer |
Pro Tips & Best Practices
- Measure overhangs; they meaningfully increase area.
- Increase waste for hips/valleys and small cut pieces.
- Verify bundle coverage; architectural shingles differ from 3-tab.
- Include ridge vent length and cap shingles.
- Check local code for ice/water and underlayment requirements.
Related Calculators
FAQ
Q: How do I measure roof area?
A: Multiply building footprint by roof pitch factor or measure each plane and sum; include overhangs.
Q: What is a roofing square?
A: A roofing square is 100 square feet; shingles and underlayment are often sold by the square.
Q: How much waste should I add?
A: Add 10-15% for cuts and starter/hip/ridge shingles; complex roofs may need more.
Q: Which pitch factor do I use?
A: Common factors: 4/12 ~ 1.054, 6/12 ~ 1.118, 8/12 ~ 1.202; steeper roofs have higher factors.
Q: What about underlayment and nails?
A: Include felt/synthetic underlayment area, ice & water shield for eaves/valleys, drip edge, flashing, and nails by the coil/box.
Call to Action
Enter footprint, pitch, and waste to get accurate squares and materials—price it locally and plan deliveries confidently.