9/12 Roof Pitch

A 9/12 roof rises 9 inches for every 12 inches of horizontal run: 36.87°, a 75.0% slope, and 25.0% more surface than its footprint.

9/12 pitch at a glance
Measure	9/12 value
Angle	36.87°
Slope percent	75.0%
Rise per foot of run	9 in
Pitch multiplier (area factor)	1.2500
Hip/valley factor	1.6008
Common rafter length per foot of run	15"
Plumb cut / seat cut	36.9° / 53.1°

Where you see a 9/12 roof

Typical uses: traditional and Victorian-style homes and attic bonus rooms. A 9/12 pitch is a 3-4-5 triangle in disguise: rise 9, run 12, slope 15. That makes the multiplier exactly 1.25, so the roof area is the footprint plus a quarter, and a rafter with a 12 ft run is exactly 15 ft long before the overhang.

Roof area at 9/12

9/12 formulas

Angle = arctan(9 ÷ 12) = 36.87° Multiplier = √(9² + 12²) ÷ 12 = 1.2500 Roof area = footprint × 1.2500 Rafter = run × 1.2500 Ridge height = run × 9 ÷ 12

Worked examples

Roof area. A 48 × 30 ft house with 1 ft overhangs has a 50 × 32 = 1,600 sq ft footprint. At 9/12: 1,600 × 1.2500 = 2,000 sq ft, or 20.0 squares before waste.

Rafter. A 28 ft span with a 1-1/2" ridge board has a 13.938 ft run. Line length = 13.938 × 1.2500 = 17' 5-1/16"; add an 18" overhang (1' 10-1/2" along the slope) for 19' 3-9/16". The ridge sits 10' 6" above the plate line. Try other spans in the rafter calculator.

9/12 rafter lengths and ridge heights

Common rafters at 9/12, measured to the center of the ridge
Building span	Run	Rafter (no overhang)	Ridge rise
16 ft	8 ft	10' 0"	6' 0"
20 ft	10 ft	12' 6"	7' 6"
24 ft	12 ft	15' 0"	9' 0"
28 ft	14 ft	17' 6"	10' 6"
32 ft	16 ft	20' 0"	12' 0"
36 ft	18 ft	22' 6"	13' 6"

Roof area by footprint at 9/12

Footprint to roof area at 9/12
Footprint (incl. overhang)	Roof area	Squares
1,000 sq ft	1,250 sq ft	12.5
1,500 sq ft	1,875 sq ft	18.8
2,000 sq ft	2,500 sq ft	25.0
2,500 sq ft	3,125 sq ft	31.3
3,000 sq ft	3,750 sq ft	37.5

Materials and walkability

Shingles: Yes. 4/12 and steeper takes a standard shingle installation.
Walkable? Not without equipment. Plan on roof jacks, harnesses and anchors.

← 8/12 pitch · 10/12 pitch → · All pitches in degrees

Frequently asked questions

How many degrees is a 9/12 roof pitch?

A 9/12 roof pitch is 36.87 degrees.

What is the multiplier for a 9/12 pitch?

The pitch multiplier for 9/12 is 1.2500. Multiply the footprint area or horizontal run by it to get the sloped area or rafter length.

Can you put shingles on a 9/12 roof?

Yes. 4/12 and steeper takes a standard shingle installation.

Is a 9/12 roof walkable?

Not without equipment. Plan on roof jacks, harnesses and anchors.

Last reviewed 2026-10-10. Results are estimates for planning; confirm quantities with your supplier and requirements with your local building code and the manufacturer's instructions.