4/12 Roof Pitch

A 4/12 roof (also written 4:12 or "4 on 12") rises 4 inches for every 12 inches of horizontal run: 18.43°, a 33.3% slope, and 5.4% more surface than its footprint.

4/12 pitch at a glance
Measure	4/12 value
Angle	18.43°
Slope percent	33.3%
Rise per foot of run	4 in
Pitch multiplier (area factor)	1.0541
Hip/valley factor	1.4530
Common rafter length per foot of run	12-5/8"
Plumb cut / seat cut	18.4° / 71.6°

Where you see a 4/12 roof

Typical uses: ranch and split-level homes, garages and porch roofs. A 4/12 roof is where standard shingle installation starts: a single layer of underlayment is fine from 4/12 up under the IRC. It is gentle enough to walk comfortably, so labor is at the low end, and the pitch adds only about 5% to the footprint area.

Roof area at 4/12

4/12 formulas

Angle = arctan(4 ÷ 12) = 18.43° Multiplier = √(4² + 12²) ÷ 12 = 1.0541 Roof area = footprint × 1.0541 Rafter = run × 1.0541 Ridge height = run × 4 ÷ 12

Worked examples

Roof area. A 48 × 30 ft house with 1 ft overhangs has a 50 × 32 = 1,600 sq ft footprint. At 4/12: 1,600 × 1.0541 = 1,687 sq ft, or 16.9 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 × 1.0541 = 14' 8-5/16"; add an 18" overhang (1' 7" along the slope) for 16' 3-1/4". The ridge sits 4' 8" above the plate line. Try other spans in the rafter calculator.

4/12 rafter lengths and ridge heights

Common rafters at 4/12, measured to the center of the ridge
Building span	Run	Rafter (no overhang)	Ridge rise
16 ft	8 ft	8' 5-3/16"	2' 8"
20 ft	10 ft	10' 6-1/2"	3' 4"
24 ft	12 ft	12' 7-13/16"	4' 0"
28 ft	14 ft	14' 9-1/16"	4' 8"
32 ft	16 ft	16' 10-3/8"	5' 4"
36 ft	18 ft	18' 11-11/16"	6' 0"

Roof area by footprint at 4/12

Footprint to roof area at 4/12
Footprint (incl. overhang)	Roof area	Squares
1,000 sq ft	1,054 sq ft	10.5
1,500 sq ft	1,581 sq ft	15.8
2,000 sq ft	2,108 sq ft	21.1
2,500 sq ft	2,635 sq ft	26.4
3,000 sq ft	3,162 sq ft	31.6

Materials and walkability

Shingles: Yes. 4/12 and steeper takes a standard shingle installation.
Walkable? Generally yes, in dry conditions with proper footwear and fall protection where required.
OSHA class: Low-slope (OSHA): OSHA treats anything steeper than 4/12 as a steep roof for fall-protection rules.

Roofing materials allowed on a 4/12 roof

Minimum pitch by roofing material vs a 4/12 roof (IRC R905)
Roof covering	Code minimum	OK at 4/12?
Standing-seam metal panels	0.25/12 (IRC R905.10.2)	Yes
Built-up, modified bitumen, single-ply membrane (TPO, EPDM, PVC)	0.25/12 (IRC R905.9, R905.11, R905.12)	Yes
Lapped metal panels with lap sealant	0.5/12 (IRC R905.10.2)	Yes
Mineral-surfaced roll roofing	1/12 (IRC R905.5.2)	Yes
Asphalt shingles	2/12 (IRC R905.2.2)	Yes
Clay and concrete tile	2.5/12 (IRC R905.3.2)	Yes
Metal roof shingles	3/12 (IRC R905.4.2)	Yes
Lapped metal panels, no sealant (exposed-fastener)	3/12 (IRC R905.10.2)	Yes
Wood shingles and shakes	3/12 (IRC R905.7, R905.8)	Yes
Slate	4/12 (IRC R905.6.2)	Yes

Sources

International Code Council, International Residential Code (2021 and 2024), Section R905 minimum slopes, as summarized in IRC 2024 Chapter 9 (UpCodes) and the MyBuildingPermit residential re-roof checklist. Local amendments and manufacturer instructions can be stricter.
OSHA, 29 CFR 1926.500(b): a low-slope roof is 4 in 12 or less; a steep roof is greater than 4 in 12. 1926.501(b)(13) requires fall protection for residential construction work 6 ft or more above a lower level.

← 3/12 pitch · 5/12 pitch → · All pitches in degrees

Frequently asked questions

How many degrees is a 4/12 roof pitch?

A 4/12 roof pitch is 18.43 degrees.

What is the multiplier for a 4/12 pitch?

The pitch multiplier for 4/12 is 1.0541. Multiply the footprint area or horizontal run by it to get the sloped area or rafter length.

Can you put shingles on a 4/12 roof?

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

Is a 4/12 roof walkable?

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

Last reviewed 2026-10-21. Results are estimates for planning; confirm quantities with your supplier and requirements with your local building code and the manufacturer's instructions.