Construction

Roof Pitch Calculator

Roof pitch (also called slope) determines what roofing materials you can use, how much labor a roofing job takes, how a house looks architecturally, and how rafters get cut. US convention expresses it as rise/run — "6/12 pitch" means the roof rises 6 inches for every 12 inches of horizontal run. This calculator converts between rise/run, angle in degrees, and percent slope. Optional horizontal run input also gives you rafter length for the framing math. Standard residential pitches: 4/12 (minimum for asphalt shingles), 6/12 (most common), 9/12 (steep, more labor), 12/12 (very steep, 45°, dramatic).

Enter the rise (inches per 12 inches of run).

Common pitches

Rise/Run	Angle	Use
2/12	9.5°	Low-slope, special membrane needed
4/12	18.4°	Min for asphalt shingles
6/12	26.6°	Most common residential
9/12	36.9°	Steep — extra labor
12/12	45°	Very steep, dramatic

Pitch by material compatibility

0-1/12 (flat): Built-up roof (BUR), modified bitumen, EPDM rubber, TPO / PVC single-ply membranes only. No shingles.
1-2/12 (very low slope): Same membrane systems. Or shingles ONLY with double underlayment + ice-and-water shield across entire roof.
2-4/12 (low slope): Standing seam metal works well. Asphalt shingles with full ice-and-water shield underlayment per manufacturer requirements.
4-21/12 (residential standard): Asphalt shingles, metal, tile, slate — all work.
21/12+ (very steep / wall): Specialty roofing only — tiles or cedar shake for steep walls / mansard. Asphalt shingles need extra fastening.

Worked examples

6/12 pitch with 14-ft run. Angle: 26.6°. Slope: 50%. Rafter length: √(14² + 7²) = 15.65 ft. Add 1-2 ft overhang allowance = order 18-ft rafters.

9/12 pitch with 16-ft run. Angle: 36.9°. Slope: 75%. Rafter length: √(16² + 12²) = 20 ft. The 9/12 pitch dramatically increases rafter length for the same building footprint.

4/12 pitch with 20-ft run. Angle: 18.4°. Slope: 33%. Rafter length: √(20² + 6.67²) = 21.08 ft.

How to use this calculator

Rise: inches per 12" of horizontal run.
Horizontal run (optional, in feet): half the building width for a typical gable roof, or the full distance from outside wall to ridge.
Output: pitch (as rise/12), angle in degrees, slope %, rafter length.
To measure existing roof pitch: place a level on the roof with the bubble centered, measure how much the roof rises in the 12 inches the level covers. That's your pitch ratio.

FAQ

What does 6/12 mean? +

For every 12 inches of horizontal run, the roof rises 6 inches. "Rise/run" notation. So 6/12 = 6 inches up per 12 inches across = roughly 26.6° angle.

What's the minimum pitch for asphalt shingles? +

4/12 by most manufacturer specs and IRC code. Below 4/12 down to 2/12, shingles can be used with full ice-and-water shield underlayment and specific installation methods. Below 2/12, switch to standing seam metal or a single-ply membrane (TPO, EPDM, etc.).

How does pitch affect roofing cost? +

Steeper pitches cost more per square foot of roof area: more labor (slower work on steep roofs), required safety equipment, harder logistics. Roofers typically charge 1.0x for 4-6/12, 1.2x for 7-9/12, 1.5x for 10-12/12, 1.8-2x for 12/12+ and walkable mansard.

Does steeper pitch mean longer roof life? +

Generally yes — steeper roofs shed water faster, accumulate less debris, have less ice-dam risk, and are less prone to wind damage from any given storm. A 9/12 asphalt roof in moderate climate often outlives a 4/12 roof by 5-10 years.

What pitch should I choose for new construction? +

6/12 is the residential standard — balance of cost, appearance, performance. Higher (8-10/12) for traditional / colonial styles. Lower (3-5/12) for modern / craftsman. Very high (12/12+) only for distinctive architectural statements.

How do I measure roof pitch from the ground? +

Standing back from the house, hold a level vertically against the gable end at the building line. Measure horizontally from level to roof surface at exactly 12 inches up the level — that's roughly your pitch in inches. Cleaner: use a smartphone level app at the gable trim.

What's the difference between pitch and slope? +

Pitch is the rise / 12-inch run ratio (carpenter convention, US). Slope is the same ratio expressed as a percentage (slope = pitch / 12 × 100%). Angle is the same relationship in degrees. They're different ways of expressing the same geometric fact.

How does pitch affect attic space? +

Steeper pitches create dramatically more attic space. A 6/12 pitch over a 30-ft wide building gives 8 ft of headroom under the ridge — livable space if framed for it. A 9/12 pitch gives 11+ ft — full second-story potential. Low pitches (3-4/12) give minimal attic space; just enough for insulation and ventilation.