Roof Pitch Calculator
I know the
6 means a 6/12 roof
Roof pitch
6/12
- Angle
- 26.57°
- Slope
- 50%
- Ratio
- 1 : 2
- Pitch factor
- 1.118
Conventional slope: suits shingles, metal and tile, and is walkable for most roofers.
The pitch factor is the sloped length per unit of level run, √(1 + (pitch/12)²). Multiply a plan area by it to get the roof surface.
Rafters and roof area (gable roof)
- Ridge height above walls
- 7 ft
- Rafter length
- 16.77 ft
- Roof area
- 1,409 ft²
- Roofing squares
- 14.1
Rafter length runs from the ridge line to the end of the overhang along the slope, before subtracting half the ridge board or adding the plumb cut. One roofing square covers 100 ft²; add 10–15% for waste on a simple gable, more for hips and valleys.
Convert a roof pitch between rise per 12, degrees, percent slope and ratio, get the pitch factor, and for a gable roof find the ridge height, rafter length, roof area and roofing squares from the building's width, length and overhang.
Formula
Worked Example
Each rafter covers a 14 ft half-span plus 1 ft of overhang: 15 ft × 1.118 = 16.77 ft along the slope. Two slopes of 16.77 ft by 42 ft (with gable overhangs) make 1,409 ft², about 14 roofing squares before waste.
Frequently Asked Questions
How do I convert roof pitch to degrees?
Take the arctangent of the rise divided by 12. A 4/12 roof is 18.4°, 6/12 is 26.6°, 8/12 is 33.7°, 12/12 is 45° and 3/12 is 14°.
What roof pitch do shingles need?
Asphalt shingles are normally installed on slopes of 4/12 or more; from 2/12 to 4/12 manufacturers require a double underlayment. Flatter roofs need membrane roofing such as TPO, EPDM or modified bitumen.
What is a roofing square?
100 square feet of roof surface. Shingles are sold by the square, usually in three bundles; add 10–15% for waste on a simple gable and more for hips, valleys and dormers.