Roofing Calculator - Area, Pitch, Shingles and Cost
Get the exact roof surface area, pitch angle, rafter length, ridge length, underlayment and roofing materials for gable, hip, shed, flat, gambrel and pyramid roofs. Includes waste adjustment, squares, bundles and cost - all from real roofing formulas.
Advanced options
Total Roof Surface Area
Material Breakdown
| Material | Quantity | Notes |
|---|
Rafter and Framing Estimates
| Item | Estimate |
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To Use Roofing Calculator for Shingles, Tiles, Metal and Flat Roofs
Pick your roof shape, enter building dimensions and pitch, and the calculator returns every material you need to order.
Roof Pitch, Angle and Slope Factor Reference
The slope factor is the multiplier that converts plan area into actual roof surface area. Multiply plan area by the slope factor to get roof surface.
| Pitch (rise:12) | Angle | Slope factor | Typical use |
|---|---|---|---|
| 1:12 | 4.8° | 1.003 | Low-slope membrane, flat |
| 2:12 | 9.5° | 1.014 | Minimum for shingles with double underlay |
| 3:12 | 14.0° | 1.031 | Shallow pitched roof |
| 4:12 | 18.4° | 1.054 | Standard minimum for shingles |
| 5:12 | 22.6° | 1.083 | Common residential |
| 6:12 | 26.6° | 1.118 | Very common residential |
| 7:12 | 30.3° | 1.158 | Medium pitch |
| 8:12 | 33.7° | 1.202 | Steeper residential |
| 9:12 | 36.9° | 1.250 | Steep residential |
| 10:12 | 39.8° | 1.302 | Steep, tile roofs |
| 12:12 | 45.0° | 1.414 | Very steep, decorative |
Roofing Material Coverage Guide
Every roofing material has its own coverage rate and packaging. These are the standards the calculator uses.
| Material | Coverage per unit | Standard package | Lifespan |
|---|---|---|---|
| Asphalt shingles (3-tab) | 1 square = 100 ft² (9.29 m²) | 3 bundles per square | 15 - 20 years |
| Architectural shingles | 1 square = 100 ft² | 3 - 4 bundles per square | 25 - 30 years |
| Standing seam metal | Panel width 300 - 500 mm | Cut to length on site | 40 - 60 years |
| Corrugated metal sheet | 1 sheet = 1 × 2 m = 2 m² | Per sheet | 30 - 40 years |
| Clay / concrete tiles | 10.5 tiles per m² | Pallet of 200 - 300 | 50+ years |
| Slate tiles | 20 tiles per m² | Pallet or crate | 80 - 100 years |
| Wood shakes | 80 shakes per m² | Bundle of 100 | 25 - 40 years |
| EPDM membrane | Roll 1.5 m wide × 15 - 30 m | Per roll | 20 - 30 years |
| Underlayment (felt / synthetic) | 1 roll = 100 m² | Roll | Same as roof |
| Ridge cap shingles | 1 bundle = 10 - 12 linear m | Per bundle | Same as shingles |
How the Roofing Calculator Works
Every result uses the standard roofing estimation method used by contractors and quantity surveyors. Here is the exact process.
- Plan area is building footprint plus overhang, calculated from length × width.
- Slope factor converts plan area to actual roof surface. It equals 1/cos(pitch angle) or √(pitch²+144)/12 for rise:12 pitches.
- Roof surface area = plan area × slope factor. This is the area you actually cover.
- Ridge length depends on roof shape - gable ridge = building length, hip ridge = length - width, shed and flat have no ridge.
- Rafter length = √(run² + rise²) where run is half the building width (gable) or full width (shed), plus overhang.
- Roofing squares = roof surface area in ft² / 100. One square = 9.29 m².
- Material counts scale from roof surface area using each material's coverage rate.
- Wastage is added as a percentage so you have spare material on site.
Roofing Formula and Worked Example
These are the exact formulas used by the calculator. Bookmark this section if you want to verify the numbers yourself.
- Plan area = (length + 2 × overhang) × (width + 2 × overhang)
- Pitch angle = arctan(rise / 12) for rise:12 pitch
- Slope factor = 1 / cos(pitch angle)
- Roof surface = plan area × slope factor
- Rafter length = √((width/2)² + ((width/2) × rise/12)²) + overhang
- Roofing squares = roof surface (ft²) / 100
- Shingle bundles = squares × 3
- Ridge cap bundles = ridge length / 10 - 12 linear m
- Underlayment rolls = roof surface / 100 m²
Worked example: A 10 m × 6 m house with 5:12 pitch and 450 mm overhangs. Plan area = (10 + 0.9) × (6 + 0.9) = 75.21 m². Pitch angle = arctan(5/12) = 22.6°. Slope factor = 1/cos(22.6°) = 1.083. Roof surface = 75.21 × 1.083 = 81.46 m² = 876.8 ft² = 8.77 squares. Add 10% waste = 9.65 squares. Shingle bundles = 9.65 × 3 = 29 bundles (round up to 30). Ridge length = 10 m. Ridge caps = 10 / 12 = 1 bundle. Rafter length for half-width 3 m with 5:12 pitch = √(3² + 1.25²) + 0.45 = 3.25 + 0.45 = 3.7 m.
Frequently Asked Questions About Roofing Calculation
How do I calculate the area of my roof?
Multiply the building footprint (length × width) by the slope factor for your pitch. For a 6:12 pitch, the slope factor is 1.118. So a 100 m² footprint becomes 112 m² of roof surface. Add eaves overhang to the plan area first. The calculator above does all of this automatically from your dimensions.
What is a roofing square?
A roofing square is 100 square feet of roof surface (about 9.29 m²). It is the standard unit for ordering shingles, felt and labour. A typical 3-bedroom house has 20 - 30 squares of roof. When you order shingles, you order by the square - usually 3 bundles per square for standard 3-tab shingles.
How many bundles of shingles do I need?
Standard 3-tab asphalt shingles come in 3 bundles per square. So if your roof is 25 squares, you need 75 bundles. Architectural shingles also come in 3 bundles per square in most cases. Always add 10% for waste and cuts. The calculator outputs this automatically once you enter the roof dimensions.
How much does a new roof cost?
Cost varies widely by material and region. Asphalt shingle replacement typically costs $3 - $8 per square foot installed. Metal roofing costs $8 - $15 per square foot installed. Clay tile and slate cost $15 - $30 per square foot installed. The calculator gives material-only cost - add labour at 40 - 60% of total for a professional job.
What is the minimum roof pitch for shingles?
Asphalt shingles require a minimum pitch of 4:12 (18.4 degrees) for standard installation. Between 2:12 and 4:12 you must double the underlayment and use special low-slope techniques. Below 2:12 you should use a membrane roofing system instead. The calculator flags pitches that are too low for shingles.
How do I calculate rafter length?
Rafter length = √(run² + rise²) + overhang. For a gable roof, run is half the building width. Rise = run × pitch/12. For a 6 m wide building with 6:12 pitch, run = 3 m, rise = 3 × 6/12 = 1.5 m. Rafter = √(9 + 2.25) = 3.35 m, plus 0.45 m overhang = 3.8 m total. The calculator handles all standard shapes.
How much underlayment do I need?
Standard underlayment rolls cover 100 m² (about 10 squares). For a 200 m² roof, you need 2 rolls minimum, or 3 rolls with overlap and waste. For low-slope roofs (under 4:12), you need double layers in some regions. Always check your local building code for specific requirements.
What is the difference between gable, hip and shed roofs?
A gable roof has two sloped sides that meet at a ridge, leaving triangular walls at the ends. A hip roof slopes down on all four sides, forming a ridge shorter than the building. A shed roof (or lean-to) has a single slope, often attached to a taller wall. Each shape has different rafter and ridge calculations.
How do I calculate ridge length?
For a gable roof, ridge length = building length. For a hip roof, ridge length = building length - building width (if length > width). For a shed roof and flat roof, there is no ridge. For a pyramid roof, there is a point not a ridge. The calculator outputs the correct ridge length for your roof shape.
How many nails per square of shingles?
Standard asphalt shingles use 320 nails per square (4 nails per shingle, 80 shingles per square). In high-wind areas, use 6 nails per shingle, giving 480 nails per square. Nails are usually 25 - 32 mm roofing nails with large heads. The calculator gives the estimated nail weight for your roof area.
Do I need drip edge on my roof?
Yes, in most modern codes. Drip edge is a metal flashing that goes along the eaves and gables to direct water away from the fascia and prevent rot. You need enough to cover the full perimeter of the roof. For a 10 m × 6 m house with overhang, that is about 40 linear metres of drip edge.
What is the best pitch for a metal roof?
Standing seam metal roofing works at pitches as low as 1:12 (some systems claim 0.5:12). Corrugated metal generally needs 3:12 or steeper. The advantages of steeper pitches are better drainage, more headroom and classic appearance. Metal roofs shed snow well at any pitch, unlike shingles.
How long does a roof last?
Lifespan depends on material: asphalt shingles 15 - 30 years, metal roofing 40 - 70 years, clay tile 50 - 100 years, slate 80 - 150 years, EPDM membrane 20 - 30 years. Climate and installation quality affect the actual lifespan significantly. A well-installed roof in a mild climate lasts longer than the same roof in a harsh environment.
How do I measure a roof without climbing on it?
Use the footprint method: measure the building outline on the ground, add the overhang on all sides, then multiply by the slope factor for your pitch. This gives you the roof surface area within 5%. The slope factor is what makes this work - it accounts for the extra surface area caused by the pitch. The calculator uses exactly this method.
References & Standards
- ASTM D3462 - Standard Specification for Asphalt Shingles Made from Glass Felt
- ASTM D7158 - Standard Test Method for Wind Resistance of Asphalt Shingles
- ASTM D3161 - Standard Test Method for Wind-Resistance of Asphalt Shingles
- BS 5534 - Code of practice for slating and tiling
- BS EN 490 - Concrete roofing tiles and fittings
- BS EN 1304 - Clay roofing tiles and fittings
- International Residential Code (IRC) Chapter 9 - Roof Assemblies
- AS 1562.1 - Design and installation of sheet roof and wall cladding (Australia)
- NIS 550 - Nigerian Industrial Standard Building Code