Roofing Calculator
Roofing Area Calculator
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Roofing Material Calculator
Already know the roof area? Enter it to convert to roofing squares and the number of bundles of standard asphalt shingles, with and without an allowance for waste. Most three-tab and architectural shingles come three bundles to a square, though heavier designer shingles can take four or five, so check the wrapper.
Press Calculate to see the results.
This roofing calculator estimates the area of a roof from the house's base area, its pitch and the eave overhang, and converts any roof area into roofing squares and bundles of shingles.
Roofers measure in squares: one square is 100 square feet of roof surface. A roof is always larger than the floor beneath it, because it slopes and usually overhangs the walls. To estimate it, the calculator takes the house's base area, adds the eave overhang on every side, and multiplies by a slope factor that depends on the pitch. A 2,000-square-foot footprint with a 1-foot overhang and a 6/12 pitch gives about 2,441 square feet of roof, or 24.4 squares.
Order more material than the measured area. Shingles are cut at edges, hips, valleys and around chimneys and vents, and starter strips and ridge caps add more. About 10% extra is typical for a simple gable roof and 15% or more for a roof with many hips and valleys.
Measuring from the ground is safer than climbing onto a roof. Measure the outside of the house, calculate the footprint, and estimate the overhang from below. For complex roofs with several sections at different pitches, calculate each part separately and add them together, or use aerial measurement reports that many roofing suppliers offer.
Roof Pitch
Pitch describes how steep a roof is, written in the US as inches of vertical rise per 12 inches of horizontal run. A 6/12 roof climbs 6 inches for every foot it extends inward, an angle of about 26.6 degrees. You can measure it with a level and a tape: hold a 12-inch level horizontally against a rafter or the roof surface and measure straight up from the 12-inch mark to the roof.
The slope factor converts footprint area to roof area. It equals √(1 + (rise ÷ 12)²), the length of the sloped side of a right triangle with a run of one. Flat and low-slope roofs below about 3/12 need membrane roofing rather than shingles, since water drains too slowly for overlapping shingles to shed it; most asphalt shingle manufacturers require at least 2/12 with special underlayment and prefer 4/12 or steeper. Conventional pitches from 4/12 to 9/12 are walkable and the most common on houses. Steep roofs above about 9/12 shed water and snow well but require safety equipment to work on, and installers usually charge more for them.
Pitch also affects how a house looks, how much attic space it has and which materials suit it. Slate, tile and wood shakes generally need steeper slopes than metal panels, which can be installed on quite low pitches.
| Pitch | Angle | Slope factor |
|---|---|---|
| 1/12 | 4.76° | 1.0035 |
| 2/12 | 9.46° | 1.0138 |
| 3/12 | 14.04° | 1.0308 |
| 4/12 | 18.43° | 1.0541 |
| 5/12 | 22.62° | 1.0833 |
| 6/12 | 26.57° | 1.118 |
| 7/12 | 30.26° | 1.1577 |
| 8/12 | 33.69° | 1.2019 |
| 9/12 | 36.87° | 1.25 |
| 10/12 | 39.81° | 1.3017 |
| 11/12 | 42.51° | 1.3566 |
| 12/12 | 45° | 1.4142 |
| 15/12 | 51.34° | 1.6008 |
| 18/12 | 56.31° | 1.8028 |
| 24/12 | 63.43° | 2.2361 |
Frequently asked questions
How many squares is my roof?
Divide the roof area in square feet by 100. A 2,400-square-foot roof is 24 squares.
How many bundles of shingles are in a square?
Usually three for standard three-tab and architectural asphalt shingles. Some heavier shingles need four or five bundles per square.
How do I calculate roof area from the floor area?
Add the overhang to the footprint and multiply by the slope factor for the pitch, √(1 + (pitch ÷ 12)²). For a 6/12 roof the factor is 1.118.
What is a 6/12 roof pitch in degrees?
About 26.57 degrees. The angle is the arctangent of 6 ÷ 12.
How many square feet are in a roofing square?
One roofing square is 100 square feet of roof surface, an area of 10 × 10 feet or about 9.29 square meters. Divide the roof area by 100 to get the number of squares, then add about 10% for waste on a simple gable roof.
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