Slope percentage is rise divided by run, expressed as a percentage. A 6/12 roof is a 50% slope, 4/12 is 33.3% and 12/12 is 100%. A quarter inch per foot — the minimum fall on a low-slope roof — is about 2.08%.
The Roof Slope Calculator converts between three ways of expressing roof slope: angle in degrees, X-in-12 pitch ratio, and slope multiplier. A 4/12 pitch is 18.4° and has a multiplier of 1.054; a 12/12 pitch is 45° and has a multiplier of 1.414. The slope multiplier converts flat footprint area into actual sloped surface area, which is the figure you use to order shingles, underlayment, and decking. Use this tool with our Pitch Chart and Roof Area Calculator.
Slope, pitch and angle are three ways of stating the same thing. Slope percentage is rise divided by run expressed as a percentage — a 6/12 roof is a 50% slope. It is the unit drainage and civil plans use, and the one roofers use least.
| Pitch | Angle | Slope % | Multiplier | 2,000 sq ft footprint becomes |
|---|---|---|---|---|
| 1/12 | 4.8° | 8.3% | 1.0035 | 2,007 sq ft |
| 2/12 | 9.5° | 16.7% | 1.0138 | 2,028 sq ft |
| 3/12 | 14.0° | 25.0% | 1.0308 | 2,062 sq ft |
| 4/12 | 18.4° | 33.3% | 1.0541 | 2,108 sq ft |
| 5/12 | 22.6° | 41.7% | 1.0833 | 2,167 sq ft |
| 6/12 | 26.6° | 50.0% | 1.1180 | 2,236 sq ft |
| 7/12 | 30.3° | 58.3% | 1.1577 | 2,315 sq ft |
| 8/12 | 33.7° | 66.7% | 1.2019 | 2,404 sq ft |
| 9/12 | 36.9° | 75.0% | 1.2500 | 2,500 sq ft |
| 10/12 | 39.8° | 83.3% | 1.3017 | 2,603 sq ft |
| 12/12 | 45.0° | 100.0% | 1.4142 | 2,828 sq ft |
| 14/12 | 49.4° | 116.7% | 1.5366 | 3,073 sq ft |
| 16/12 | 53.1° | 133.3% | 1.6667 | 3,333 sq ft |
| 18/12 | 56.3° | 150.0% | 1.8028 | 3,606 sq ft |
| 20/12 | 59.0° | 166.7% | 1.9437 | 3,887 sq ft |
| 24/12 | 63.4° | 200.0% | 2.2361 | 4,472 sq ft |
| Covering | Minimum pitch | Notes |
|---|---|---|
| Asphalt shingles | 2/12 | Doubled underlayment required from 2/12 to 4/12 |
| Wood shakes and shingles | 3/12 | Higher in wet climates |
| Exposed-fastener metal panels | 3/12 | Some profiles need more; check the product |
| Standing-seam metal | As low as ¼ in 12 | Only with sealed seams on approved systems |
| Concrete and clay tile | 2½/12 | Underlayment does the waterproofing at low slopes |
| Single-ply membrane (EPDM, TPO, PVC) | ¼ in 12 | A fall is still required — nothing is truly flat |
Below the minimum, the covering is not permitted and no manufacturer will warrant it. That is the first thing to check on any low-slope roof before choosing a material.
Slope percentage is rise divided by run as a percentage — a 6/12 roof is a 50% slope. Pitch is the rise-over-12 ratio itself. They describe the same geometry in different units.
It depends on the covering: 2/12 for asphalt shingles, 3/12 for exposed-fastener metal and wood, 2½/12 for tile, and as low as a quarter inch per foot for sealed single-ply membrane. Below the minimum no manufacturer will warrant the material.
About 2.08%, or a 0.25/12 pitch. It is the minimum fall required on a low-slope roof so water drains rather than ponds.
It should not be. Codes require a minimum fall so water drains. A genuinely level roof ponds, and standing water shortens the life of any membrane sharply.