3/12 Roof Pitch

A 3/12 roof rises 3 inches for every 12 inches of horizontal run: 14.04°, a 25.0% slope, and 3.1% more surface than its footprint.

3/12 pitch at a glance
Measure	3/12 value
Angle	14.04°
Slope percent	25.0%
Rise per foot of run	3 in
Pitch multiplier (area factor)	1.0308
Hip/valley factor	1.4361
Common rafter length per foot of run	12-3/8"
Plumb cut / seat cut	14.0° / 76.0°

Where you see a 3/12 roof

Typical uses: ranch homes, porches, garages, sheds and pole barns. A 3/12 roof is a classic low-slope pitch for ranch houses and metal buildings. Shingles are allowed with double underlayment, and many exposed-fastener metal panels list 3/12 as their minimum without lap sealant. It is easy to walk and cheap to frame, but it gives little attic room.

Roof area at 3/12

3/12 formulas

Angle = arctan(3 ÷ 12) = 14.04° Multiplier = √(3² + 12²) ÷ 12 = 1.0308 Roof area = footprint × 1.0308 Rafter = run × 1.0308 Ridge height = run × 3 ÷ 12

Worked examples

Roof area. A 48 × 30 ft house with 1 ft overhangs has a 50 × 32 = 1,600 sq ft footprint. At 3/12: 1,600 × 1.0308 = 1,649 sq ft, or 16.5 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 × 1.0308 = 14' 4-3/8"; add an 18" overhang (1' 6-9/16" along the slope) for 15' 10-15/16". The ridge sits 3' 6" above the plate line. Try other spans in the rafter calculator.

3/12 rafter lengths and ridge heights

Common rafters at 3/12, measured to the center of the ridge
Building span	Run	Rafter (no overhang)	Ridge rise
16 ft	8 ft	8' 2-15/16"	2' 0"
20 ft	10 ft	10' 3-11/16"	2' 6"
24 ft	12 ft	12' 4-7/16"	3' 0"
28 ft	14 ft	14' 5-3/16"	3' 6"
32 ft	16 ft	16' 5-15/16"	4' 0"
36 ft	18 ft	18' 6-5/8"	4' 6"

Roof area by footprint at 3/12

Footprint to roof area at 3/12
Footprint (incl. overhang)	Roof area	Squares
1,000 sq ft	1,031 sq ft	10.3
1,500 sq ft	1,546 sq ft	15.5
2,000 sq ft	2,062 sq ft	20.6
2,500 sq ft	2,577 sq ft	25.8
3,000 sq ft	3,092 sq ft	30.9

Materials and walkability

Shingles: Yes, but codes require double underlayment (or an approved equivalent) between 2/12 and 4/12.
Walkable? Generally yes, in dry conditions with proper footwear and fall protection where required.

← 2/12 pitch · 4/12 pitch → · All pitches in degrees

Frequently asked questions

How many degrees is a 3/12 roof pitch?

A 3/12 roof pitch is 14.04 degrees.

What is the multiplier for a 3/12 pitch?

The pitch multiplier for 3/12 is 1.0308. Multiply the footprint area or horizontal run by it to get the sloped area or rafter length.

Can you put shingles on a 3/12 roof?

Yes, but codes require double underlayment (or an approved equivalent) between 2/12 and 4/12.

Is a 3/12 roof walkable?

Generally yes, in dry conditions with proper footwear and fall protection where required.

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.