4/12 Roof Pitch
A 4/12 pitch rises 4 inches for every 12 inches of run: 18.43°, a 33.3% slope and a multiplier of 1.054.
- Angle18.43°
- Percent slope33.3%
- Multiplier1.0541
- Rafter per ft run12.65 in
Roof pitch
4/12 pitch
18.4° · 33.3% · ×1.054
4/12 is 18.43°, a 33.3% slope, and the roof is 5.4% larger than its footprint.
- Angle18.43°
- Percent slope33.3%
- Pitch multiplier1.0541
- Hip and valley factor1.4530
- Rafter per foot of run12.65 in
- Slope class (OSHA)Low slope (4 in 12 or less)
Pitch is rise in inches over 12 inches of run. The multiplier turns a flat measurement into sloped length: multiply the footprint area by it to get roof area.
Planning estimate, not a quote. Disclaimer
What a 4/12 pitch looks like
At 4/12 the roof sits right at the line between low slope and standard slope. It is one of the most searched pitches, and it is the point where ordinary shingle installation begins. The roof rises 4 inches for every 12 inches of run. That is a 18.43° angle, a 33.3% slope and a roof surface 5.4% larger than its footprint.
Roof area at 4/12
Multiply the footprint by 1.0541. For common footprints, with no overhang and 10% extra on the shingles:
| Footprint | Roof area | Squares | Bundles with 10% extra |
|---|---|---|---|
| 1,000 sq ft | 1,054 sq ft | 10.5 | 35 |
| 1,500 sq ft | 1,581 sq ft | 15.8 | 53 |
| 2,000 sq ft | 2,108 sq ft | 21.1 | 70 |
| 2,500 sq ft | 2,635 sq ft | 26.4 | 87 |
| 3,000 sq ft | 3,162 sq ft | 31.6 | 105 |
Rafter length at 4/12
Each foot of run adds 12.65 inches of common rafter, or 1.4530 ft of hip or valley rafter per foot of common run. For some typical runs, measured to the ridge centerline:
| Run | Rise | Rafter length |
|---|---|---|
| 4 ft | 1 ft 4 in | 4 ft 2⅝ in |
| 6 ft | 2 ft 0 in | 6 ft 3⅞ in |
| 8 ft | 2 ft 8 in | 8 ft 5¼ in |
| 10 ft | 3 ft 4 in | 10 ft 6½ in |
| 12 ft | 4 ft 0 in | 12 ft 7¾ in |
| 14 ft | 4 ft 8 in | 14 ft 9⅛ in |
| 16 ft | 5 ft 4 in | 16 ft 10⅜ in |
Roofing materials at 4/12
GAF treats slopes of 4:12 and above as standard, with single-layer underlayment. Metal Sales lists 3:12 as the minimum for its residential profiles and MBCI ½:12 for PBR, so 4/12 works for them too. Always check your product.
Can you walk a 4/12 roof?
OSHA's fall-protection rules class a roof of 4 in 12 or less as low slope, and 4/12 meets that definition. Low slope does not mean safe: wet, dusty or leaf-covered roofs are slippery, and falls from any height hurt. This is general information, not safety advice.
Frequently asked questions
What angle is a 4/12 roof pitch?
18.43 degrees, a 33.3% slope.
What is the multiplier for a 4/12 roof?
1.0541. Multiply the footprint area by it to get roof area. The hip/valley factor is 1.4530.
How much roof area does a 4/12 pitch add?
5.4% over the footprint. A 2,000 sq ft footprint becomes 2,108 sq ft of roof, 21.1 squares.
Is 4/12 a low-slope roof?
By OSHA’s definition, yes: 4 in 12 or less is low slope. GAF adds rules below 4:12, including double underlayment from 2:12 to 4:12, and gives 2:12 as the absolute minimum slope for shingles.
How much does a 4/12 roof rise over a 12-foot run?
4 feet. Over a 12-foot run the roof climbs 4 feet, which is 12 ft 7¾ in of rafter along the slope.
Other roof pitches
Related
Other roofing calculators
Sources
- OSHA 29 CFR 1926.500: definitions of low-slope and steep roofs (checked Nov 12, 2026)
- GAF: Minimum slope for shingles (checked Nov 12, 2026)
- Swanson Tool: Roof pitch reference (rafter length per foot of run) (checked Nov 12, 2026)