How do I calculate roof area from ground measurements?

Roof area = Footprint area x Pitch multiplier The pitch multiplier accounts for the slope: Multiplier = sqrt(rise² + 12²) / 12 Common multipliers: • 4/12 pitch: 1.054x • 6/12 pitch: 1.118x • 8/12 pitch: 1.202x • 12/12 pitch: 1.414x Example — 40 ft x 30 ft house, 6/12 gable roof: • Footprint: 40 x 30 = 1,200 sq ft • Slope area: 1,200 x 1.118 = 1,342 sq ft • +15% waste: 1,342 x 1.15 = 1,543 sq ft = 15.4 squares Note: Gable and hip roofs with the same footprint and pitch have the same total area.

What is a roofing square?

A roofing square is 100 square feet of roof surface. It is the standard unit used by roofing contractors and material suppliers. • 1 square = 100 sq ft • 1 square of asphalt shingles = 3 bundles • 1 bundle weighs approximately 60–80 lb for standard 3-tab, 60–90 lb for architectural shingles When ordering materials, always convert your roof area to squares first, then apply your waste factor. A 1,500 sq ft roof (after waste) = 15 squares = 45 bundles of standard asphalt shingles.

How much does a new roof cost?

US roofing costs (2025 averages, installed): • 3-tab asphalt shingles: $150–$250 per square installed • Architectural (laminated) shingles: $200–$350 per square • Metal standing seam: $600–$1,200 per square • Clay/concrete tile: $500–$1,000 per square • Slate: $800–$2,000+ per square For a typical 2,000 sq ft home with a 6/12 gable roof: • Roof area: ~2,240 sq ft = 22.4 squares + 15% waste = 25.8 squares • Architectural shingles installed: 26 x $250 = $6,500 materials + labour • Total typical range: $8,000–$15,000 for a standard reroof Labour typically accounts for 40–60% of total cost. Always get 3 quotes from licensed roofers.

How many bundles of shingles do I need?

Standard asphalt shingles: 3 bundles = 1 square = 100 sq ft of roof. Formula: Bundles = (Roof area in sq ft / 100) x 3, rounded up. Example — 1,800 sq ft roof area after waste: 1,800 / 100 = 18 squares x 3 = 54 bundles Note: Some premium architectural shingles use 4 bundles per square due to heavier weight per bundle. Check the packaging — the square footage per bundle is always printed on the label. For ridge cap shingles: measure your ridge length in linear feet and divide by 35 (one bundle covers approximately 35 linear feet of ridge).

What pitch is a typical house roof?

Common roof pitches in the US: • 2/12 – 3/12: Low slope — requires special underlayment, common on additions • 4/12: Low-moderate — common in warm-climate ranch homes and flat-country states • 5/12 – 6/12: Moderate — the most common in residential construction nationwide • 7/12 – 9/12: Steep — common in northern states with heavy snow loads • 10/12 – 12/12: Very steep — Cape Cod style, requires walk boards during installation • 12/12+: Extremely steep — rare, mostly decorative towers and dormers Steeper roofs shed water and snow more effectively but cost more to install (additional labour for steep-slope work) and use more material.

Do gable and hip roofs have the same area?

Yes — a gable roof and a hip roof with the same building footprint and the same pitch have exactly the same total sloped surface area. This often surprises people because hip roofs look more complex. The reason is that the triangular hip sections have the same area as the triangular gable ends they replace. Proof (40 x 30 ft building, 6/12 pitch): • Gable: 1,200 sq ft footprint x 1.118 = 1,342 sq ft • Hip: 1,200 sq ft footprint x 1.118 = 1,342 sq ft Hip roofs do require more waste allowance (20% vs 10–15% for gable) due to more hip and valley cuts. And hip roofs require more hip ridge material. But the raw area is identical.

Roof Area Calculator — Squares, Bundles & Cost

The Roof Area Calculator works out the exact sloped surface area of any roof from your building footprint measurements. Select your roof type — Gable, Hip, Shed, or Flat — enter your pitch as rise over run (e.g. 6/12), input your building length and width in feet or metres, and the calculator instantly outputs total ro..

ROOF DETAILS

ROOF TYPE

ROOF PITCH (rise per 12" run)

6/12 pitch = 26.6° angle · 1.1180× multiplier · Moderate slope — most common

BUILDING LENGTH (feet) — longest dimension

BUILDING WIDTH (feet) — shorter dimension

WASTE / OVERAGE (%)

SHINGLE PRICE PER SQUARE (optional)

1 square = 100 sq ft · 3-tab asphalt: $80–$120/sq · Architectural: $100–$150/sq

RESULTS — GABLE ROOF · 6/12

ROOF AREA (incl. 15% waste)

1,543 sq ft

ROOFING SQUARES

15.43 squares

SHINGLE BUNDLES

bundles (3/square)

UNDERLAY ROLLS

rolls (4sq/roll)

ROOF TYPE — GABLE · 6/12 pitch (26.6°)

ROOF SUMMARY

Footprint area1,200 sq ft

Roof slope area (net)1,342 sq ft

Roof area +15% waste1,543 sq ft

Roofing squares15.43 squares

Pitch multiplier1.1180x

Rafter length (approx.)16.8 ft

Asphalt bundles (3/sq)47

Underlay rolls (4sq/roll)4

PITCH MULTIPLIER REFERENCE

2/12 — Low slope1.0138×

4/12 — Low-moderate1.0541×

6/12 — Moderate — most common1.1180×

8/12 — Steep1.2019×

12/12 — Very steep1.4142×

KEY FACTS

1 square = 100 sq ft of roof

1 square = 3 bundles of shingles

Gable & hip: same area for same footprint

Waste: 10% gable · 15% standard · 20% hip

3-tab asphalt: $80–$120/square (2025)

Architectural shingles: $100–$150/square

Labour: $150–$300/square installed

Created with❤️byeaglecalculator.com

HOW TO USE

1
Select your roof type: Gable (two slopes meeting at a central ridge — the most common), Hip (four slopes, all meeting at the ridge — common in hurricane zones), Shed or lean-to (single slope), or Flat. A 3D preview of your selected roof shape updates in the panel on the right.
2
Enter your roof pitch as rise over run. A 6/12 pitch means the roof rises 6 inches for every 12 inches of horizontal run. Use the preset buttons for the most common pitches. The calculator shows you the exact pitch angle in degrees and the pitch multiplier — the factor by which sloped area exceeds footprint area.
3
Enter your building's footprint dimensions — Length (the longest wall) and Width (the shorter wall). These are the exterior footprint measurements at ground level, not the rafter lengths. The calculator applies the pitch multiplier to convert footprint to actual sloped roof area automatically.
4
Select your waste allowance: 10% for a simple gable roof with no hips or valleys, 15% for a standard residential roof, 20% for a hip roof or any roof with dormers, valleys, or complex features. More cuts = more waste.
5
Optionally enter your shingle price per square (1 square = 100 sq ft) to get a material cost estimate. Read your results: total roof area, roofing squares, shingle bundle count (3 bundles per square for standard asphalt shingles), felt underlay rolls, and total material cost.

WORKED EXAMPLE

Calculating roof area for a 40 ft x 28 ft house, gable roof, 6/12 pitch: Step 1: Calculate building footprint 40 ft x 28 ft = 1,120 sq ft Step 2: Find the pitch multiplier Pitch multiplier = sqrt(6² + 12²) / 12 = sqrt(36 + 144) / 12 = sqrt(180) / 12 = 13.416 / 12 = 1.118 Step 3: Calculate sloped roof area 1,120 sq ft x 1.118 = 1,252 sq ft Step 4: Add 15% waste 1,252 x 1.15 = 1,440 sq ft Step 5: Convert to roofing squares 1,440 / 100 = 14.4 squares — order 15 squares Step 6: Shingle bundles (3 per square) 15 squares x 3 = 45 bundles Step 7: Felt underlay (1 roll per 4 squares) ceil(14.4 / 4) = 4 rolls Step 8: Rafter length (for material ordering) Run = 28 / 2 = 14 ft Rafter = sqrt(14² + (14 x 6/12)²) = sqrt(196 + 49) = sqrt(245) = 15.65 ft Step 9: Material cost at $120/square 14.4 squares x $120 = $1,728 for shingles only

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Last updated: April 29, 2026 · Formula verified by EagleCalculator team · Eagle-eyed accuracy for every calculation.