Roofing Calculator

Estimate shingles, underlayment, flashing, and materials needed for roof replacement projects.

Roofing Calculator

Enter your roof dimensions and specifications to calculate materials needed for your project.

Roof Dimensions

Roof Pitch

Roof Type

Shingle Type

Underlayment

Flashing & Accessories

Measure perimeter of roof for drip edge

Waste Factors

Extra shingles for cuts, starter course, ridge caps, and mistakes
Extra underlayment for overlaps and cuts

Existing Roof

How to Use the Roofing Calculator

  1. Measure Your Roof

    Measure the length (eave to ridge) and width (across the house) of your roof. For complex roofs, measure each section separately.

  2. Determine Roof Pitch

    Find your roof pitch (slope). Common residential roofs are 4/12 to 6/12 pitch. Pitch affects roof area calculations.

  3. Select Roof Type

    Choose your roof style (gable, hip, shed, etc.). Different roof types have different area calculations.

  4. Choose Shingle Type

    Select your shingle material. Different shingles have different coverage rates and bundle sizes.

  5. Select Underlayment & Flashing

    Choose underlayment type and flashing materials based on your climate and roofing needs.

  6. Account for Existing Roof

    Specify existing roof layers to determine if tear-off is needed and calculate disposal requirements.

  7. Add Waste Factors

    Include 10-20% extra shingles for cuts, starter course, ridge caps, and mistakes.

  8. Calculate

    Click "Calculate Roofing Materials" to get your material list with quantities and estimated costs.

Practical Example: Calculating a 30×40 Hip Roof

Let's calculate materials for a typical 30×40 foot hip roof with 4/12 pitch:

Inputs:

  • Dimensions: 30×40 feet (hip roof)
  • Pitch: 4/12
  • Shingle Type: Architectural asphalt shingles
  • Underlayment: Synthetic underlayment
  • Shingle Waste: 15%
  • Existing Layers: 2 layers (tear-off required)

Calculations:

  1. Base area: 30 × 40 = 1,200 sq ft
  2. Pitch factor for 4/12: 1.054
  3. Actual roof area: 1,200 × 1.054 = 1,264.8 sq ft
  4. Roofing squares: 1,264.8 ÷ 100 = 12.65 squares
  5. Bundles needed: 12.65 × 3 bundles/square = 37.95 bundles
  6. With waste: 37.95 × 1.15 = 43.64 bundles (44 bundles)
  7. Underlayment: ~13 rolls (based on coverage)
  8. Flashing/drip edge: ~140 linear feet

Result:

You would need approximately 44 bundles of architectural shingles, 13 rolls of synthetic underlayment, 140 feet of drip edge/flashing, and roofing nails for a 30×40 hip roof.

Pro Tip: Always check local building codes for roofing requirements, especially in high-wind or wildfire-prone areas. Many areas now require specific fastening patterns, underlayment types, or fire-rated materials.

Roofing Calculator FAQ

What is a "roofing square"? +

A roofing square is a unit of measurement equal to 100 square feet of roof area. Roofing materials (shingles, underlayment) are typically sold by the square rather than by square foot.

  • 1 roofing square = 100 square feet
  • Shingles: Typically 3 bundles per square
  • Underlayment: Typically 1-2 rolls per square
  • Formula: Squares = Total roof area (sq ft) ÷ 100
Example: A 2,000 sq ft roof = 20 roofing squares.

How does roof pitch affect material calculations? +

Roof pitch (slope) increases the actual surface area compared to the flat footprint. Use these pitch multipliers:

  • 3/12 pitch: Multiply flat area by 1.031
  • 4/12 pitch: Multiply by 1.054
  • 5/12 pitch: Multiply by 1.083
  • 6/12 pitch: Multiply by 1.118
  • 7/12 pitch: Multiply by 1.158
  • 8/12 pitch: Multiply by 1.202
  • 9/12 pitch: Multiply by 1.250
  • 10/12 pitch: Multiply by 1.302
  • 12/12 pitch: Multiply by 1.414
Example: A 1,000 sq ft house with 6/12 pitch roof: 1,000 × 1.118 = 1,118 sq ft of actual roof area.

How many bundles of shingles per square? +

Bundle coverage varies by shingle type:

  • 3-Tab Shingles: 3 bundles per square (standard)
  • Architectural Shingles: 3-4 bundles per square (check manufacturer)
  • Premium/Designer Shingles: 4-5 bundles per square
  • Metal Roofing: Sold by square foot or panel, not bundles
  • Tile/Slate: Sold by piece count per square
Always check the manufacturer's specifications for exact coverage. Most bundles cover approximately 33.3 square feet (1/3 of a square).

Should I tear off old shingles or roof over them? +

Consider these factors when deciding:

  • Tear-off Advantages:
    • Allows inspection of roof deck
    • Better adhesion for new shingles
    • Reduces weight on structure
    • Required by most building codes for 3+ layers
    • Warranty compliance for many shingles
  • Roof-over Advantages:
    • Lower cost (no disposal fees)
    • Faster installation
    • Provides extra insulation layer
    • Can be done in colder weather
Most professionals recommend tear-off for long-term performance and warranty protection. Check local building codes for limitations.