Roofing Calculator
Calculate the area of a sloped roof and estimate the amount of roofing material needed. Enter your house footprint dimensions and roof pitch to compute the total roof surface area, or skip directly to the material calculator using a known roof area.
Roofing Area Calculator
Roofing Material Calculator
What is Roof Pitch?
Roof pitch (or roof slope) measures how steep a roof is. It is expressed as a ratio of the vertical rise to the horizontal run, typically written as "X/12". For example, a 6/12 pitch means the roof rises 6 inches for every 12 inches of horizontal run.
The pitch affects both the aesthetic appearance of a home and its functional performance. Steeper roofs shed water and snow more effectively but require more materials and are more expensive to install. They also provide better attic ventilation and can accommodate additional living space.
θ = roof angle, Pitch = Rise / Run, Angle = arctan(Pitch / 12)
How Roof Pitch Affects Area
The steeper the roof pitch, the greater the surface area of the roof for the same house footprint. This is because the sloped surface is longer than the horizontal projection. The correction factor increases with pitch:
| Pitch | Angle | Factor |
|---|---|---|
| 3/12 | 14.0° | 1.031 |
| 4/12 | 18.4° | 1.054 |
| 5/12 | 22.6° | 1.083 |
| 6/12 | 26.6° | 1.118 |
| 7/12 | 30.3° | 1.158 |
| 8/12 | 33.7° | 1.202 |
| 9/12 | 36.9° | 1.250 |
| 10/12 | 39.8° | 1.302 |
| 12/12 | 45.0° | 1.414 |
For example, a house with a 1,000 sq ft footprint and a 6/12 pitch has a roof area of approximately 1,118 sq ft (factor of 1.118). The same house with a 12/12 pitch would have about 1,414 sq ft of roof area.
Roofing Materials
Asphalt Shingles
The most common roofing material in North America. Asphalt shingles are affordable, durable, and available in a wide range of colors and styles. They typically last 15–30 years depending on the quality and local climate. Three-tab shingles cost around $90–$120 per square installed, while architectural shingles range from $120–$180 per square.
Metal Roofing
Metal roofs are highly durable, fire-resistant, and energy-efficient. They can last 40–70 years and reflect solar heat to reduce cooling costs. Available in steel, aluminum, copper, and zinc. Installation costs range from $300–$800 per square, with premium materials like copper costing significantly more.
Tile Roofing
Clay and concrete tiles offer a distinctive look and exceptional durability with lifespans of 50–100+ years. They are heavy, requiring additional structural support, and are most common in warmer climates. Tile roofing costs $350–$1,000+ per square installed. They provide excellent fire resistance and insulation.
Wood Shake & Shingle
Wood shakes offer a natural, rustic appearance. Typically made from cedar, redwood, or pine, they provide good insulation but require more maintenance than other materials. They last 20–40 years and cost $250–$700 per square installed. Wood roofs are not recommended in fire-prone areas unless treated with fire retardant.
Rubber Membrane
Rubber roofing (EPDM or TPO) is commonly used on low-slope and flat roofs. It is lightweight, flexible, and highly waterproof. EPDM roofs can last 30–50 years and cost $300–$600 per square installed. They are popular for commercial buildings and modern residential flat roof designs.
Roof Pitch Correction Factor Table
| Pitch | Factor | Pitch | Factor |
|---|---|---|---|
| 1/12 | 1.003 | 2/12 | 1.014 |
| 3/12 | 1.031 | 4/12 | 1.054 |
| 5/12 | 1.083 | 6/12 | 1.118 |
| 7/12 | 1.158 | 8/12 | 1.202 |
| 9/12 | 1.250 | 10/12 | 1.302 |
| 11/12 | 1.357 | 12/12 | 1.414 |
| 13/12 | 1.474 | 14/12 | 1.537 |
| 15/12 | 1.601 | 16/12 | 1.667 |
| 17/12 | 1.734 | 18/12 | 1.803 |
| 19/12 | 1.873 | 20/12 | 1.944 |
| 21/12 | 2.016 | 22/12 | 2.088 |
| 23/12 | 2.162 | 24/12 | 2.236 |
How to Calculate Roof Area
To calculate your roof area manually:
- Measure the footprint of your house (length × width) to get the base area.
- Add the eaves overhang. If eaves extend 1 ft on each side, add 2 ft to both length and width.
- Determine your roof pitch (rise/run ratio such as 6/12).
- Find the correction factor for your pitch using the table above or the formula: factor = 1 / cos(arctan(pitch / 12)).
- Multiply the adjusted base area by the correction factor to get the total roof area.
For a house with a 30 ft × 40 ft footprint (1,200 sq ft), 1 ft eaves, and 6/12 pitch: adjusted base = (30+2) × (40+2) = 1,344 sq ft. Roof area = 1,344 × 1.118 = 1,503 sq ft.
Frequently Asked Questions
How do I calculate the area of my roof?
Measure the footprint area of your house (length × width), add the eaves overhang, then multiply by the roof pitch correction factor. The correction factor accounts for the slope of the roof and increases with steeper pitches. Use the Roofing Area Calculator section above for a quick calculation.
What is a roof square?
A roofing square is a unit of measure equal to 100 square feet of roof area. Roofing materials are typically quoted and sold by the square. For example, a 2,000 sq ft roof would require 20 squares of shingles. The term "square" is standard in the roofing industry for estimating material quantities and pricing.
How many shingles do I need per square?
Standard three-tab asphalt shingles come in bundles, with 3 bundles covering approximately 100 square feet (1 square). A square typically requires 3 bundles, though architectural shingles may require 4 bundles per square due to their thicker profile. Always add 10–15% for waste, cutting, and starter strips.
What is the best roof pitch for my area?
The ideal roof pitch depends on your climate. In snowy regions, steeper pitches (6/12 or higher) help shed snow and prevent ice dams. In windy areas, lower pitches (3/12 to 5/12) offer better wind resistance. In moderate climates, a 4/12 to 6/12 pitch provides a good balance of aesthetics, water shedding, and cost. Local building codes may also dictate minimum pitch requirements.
How much does a new roof cost?
Roofing costs vary widely by material, pitch, and location. Asphalt shingles typically cost $3.50 to $5.50 per square foot installed. Metal roofing ranges from $5 to $12 per square foot. Tile and slate can cost $10 to $25 per square foot. The total cost for an average 1,700 sq ft roof typically ranges from $5,000 to $15,000 including materials, labor, and disposal of the old roof.