One steepness, five ways to write it
People use pitch, slope, angle and percent as if they were the same thing. They describe one fact, how steep the roof is, in different units.
| Pitch | Also written | Angle | Percent slope | Decimal |
|---|---|---|---|---|
| 2/12 | 2:12 or 2 in 12 | 9.46° | 16.7% | 0.167 |
| 3/12 | 3:12 or 3 in 12 | 14.04° | 25.0% | 0.250 |
| 4/12 | 4:12 or 4 in 12 | 18.43° | 33.3% | 0.333 |
| 5/12 | 5:12 or 5 in 12 | 22.62° | 41.7% | 0.417 |
| 6/12 | 6:12 or 6 in 12 | 26.57° | 50.0% | 0.500 |
| 8/12 | 8:12 or 8 in 12 | 33.69° | 66.7% | 0.667 |
| 9/12 | 9:12 or 9 in 12 | 36.87° | 75.0% | 0.750 |
| 12/12 | 12:12 or 12 in 12 | 45.00° | 100.0% | 1.000 |
Why the number 12?
Builders use a 12 inch run because it matches a foot of the framing square and speed square, so the rise reads off the tool directly. The rise can be any number, including fractions such as 4.5/12, but common pitches are whole numbers.
Pitch is not the same as the angle
The biggest mistake is to read pitch as an angle. A 12/12 roof is 45 degrees, not 90, because the rise equals the run. A 6/12 roof is 26.6 degrees, not 30. The relationship is angle = arctan(pitch ÷ 12), and it is not a straight line. See the degrees to pitch chart for every angle.
Four groups by steepness
| Group | Pitch | What it means |
|---|---|---|
| Low slope | Under 2/12 | Needs a membrane or standing seam roof |
| Low pitch | 2/12 to under 4/12 | Shingles allowed with double underlayment |
| Conventional | 4/12 to 9/12 | Standard roofing, from walkable to steep to work on |
| Steep | Over 9/12 | Extra roof area, harder labor, shed snow well |
These groups follow the code minimums in the roof pitch chart. OSHA draws its own line at 4/12 for fall protection. Roofers and codes do not agree on one dividing line, so check which definition a document uses.
What pitch changes
- Roof area. A steeper roof is larger. A 12/12 roof has a 1.414 multiplier against 1.054 at 4/12, which is 34% more material for the same footprint.
- Materials. Each roofing type has a minimum slope.
- Safety and cost. Steeper roofs are harder to work on, and many roofers charge more from about 7/12 or 8/12.
Find the pitch of your own roof with the roof pitch calculator, or see what is a standard roof pitch.
Frequently asked questions
What does a 6/12 roof pitch mean?
The roof rises 6 inches for every 12 inches of horizontal run. That is 26.6 degrees, or a 50% slope.
Is roof pitch the same as roof slope?
In everyday use yes. Strictly, pitch is rise over the span and slope is rise over run, but builders write both as x/12.
What is a 45 degree roof pitch?
12/12, because the rise equals the run.