Roofing Calculator – Area, Shingles, Underlayment & Cost

How this roofing calculator works

This roofing calculator is designed to be more practical than simple “length × width” tools. It lets you:

• Add multiple roof sections (for L-shaped or complex roofs).
• Account for roof pitch, overhangs, and ridge length.
• Estimate shingles, underlayment, ridge caps, nails, and cost.
• Switch between imperial (ft, sq ft) and metric (m, m²) units.

1. Roof section geometry

Each section is treated as a simple rectangle in plan view. You enter:

• Length (horizontal run along the eave).
• Width (horizontal run from eave to eave, not along the slope).
• Overhang (optional extension beyond walls, applied to all sides).
• Pitch (e.g., 4:12, 6:12, 8:12).
• Ridge length for that section (if applicable).

The flat footprint area is:

Roof pitch is converted to a pitch factor:

For example, a 6:12 pitch has rise/run = 6/12 = 0.5, so:

The sloped area of each section is then:

The calculator sums all sections:

2. Waste factor

To account for cutting, starter courses, and offcuts, a waste percentage is applied:

Guidelines:

• 5–10% – simple gable roofs.
• 10–15% – hip roofs, some valleys.
• 15–20% – very complex roofs, many dormers/valleys.

3. Roofing squares

In North America, roofers often talk in “squares”:

4. Shingles, underlayment, ridge caps, and nails

• Shingles: You can set coverage per bundle (default 33.3 sq ft). The calculator uses:
  Bundles = Area with waste / coverage per bundle
• Underlayment: Based on coverage per roll (default 200 sq ft or 20 m²).
  Rolls = Area with waste / coverage per roll
• Ridge caps: Based on total ridge length and coverage per bundle (default 33 linear ft).
  Ridge bundles = Total ridge length / coverage per bundle
• Nails: Based on nails per 100 sq ft (default 320).
  Total nails = (Area with waste / 100) × nails per 100 sq ft

5. Cost estimation

If you enter prices, the calculator estimates:

• Shingle cost = Bundles × price per bundle.
• Underlayment cost = Rolls × price per roll.
• Ridge cap cost = Ridge bundles × price per bundle.
• Labor cost = Squares × labor rate per square (or per 10 m² in metric mode).

The total cost is the sum of all components.

Practical tips for planning a roofing project

Choosing a waste factor

• Low waste (5–8%) – simple rectangular gable, few penetrations.
• Medium waste (10–12%) – hips, valleys, skylights, chimneys.
• High waste (15–20%) – multiple dormers, complex shapes, heavy architectural shingles.

Measuring your roof safely

• Whenever possible, measure from the ground using a tape and the building footprint.
• Use satellite or aerial imagery tools for approximate dimensions.
• If you must go on the roof, use proper fall protection and never work alone.

When to call a roofing professional

This calculator is excellent for budgeting and checking contractor quotes, but you should consult a licensed roofer when:

• The roof structure may be damaged or sagging.
• Local codes require specific underlayments, ice & water shield, or ventilation.
• You are unsure about flashing details around chimneys, walls, or skylights.

FAQ

Can I use this for metal, tile, or flat roofs?

Yes. For non-shingle systems, enter the coverage per panel, sheet, or tile as the “shingle coverage per bundle” and adjust the waste factor to match manufacturer recommendations.

Does the calculator include tear-off and disposal?

No. Those costs vary widely by region and roof condition. You can approximate them by adding an extra amount to the labor rate per square.

How close will this be to a contractor’s quote?

Material quantities are usually quite close if dimensions and pitch are accurate. Total cost can differ because contractors include overhead, profit, insurance, permits, and contingencies.