Roof Pitch Calculator
Free roof pitch calculator. Convert between rise/run, angle in degrees, and rafter length. Get pitch as X/12 plus the slope factor for area calculations.
Roof Pitch Calculator
Pitch (X/12)
6/12
Angle
26.57°
Slope factor
1.118
Multiply roof footprint by this for surface area
How to use this calculator
Pick the input mode that matches what you know:
- From rise & run — measure the vertical rise over a known horizontal run (the most common DIY method)
- From angle — if you have the angle in degrees from a level, inclinometer, or app
- From rafter length & rise — if you know the rafter length and the total rise
The calculator returns three things:
- Pitch as X/12 — the standard contractor format (e.g., 6/12)
- Angle in degrees — useful for working with carpentry tools or framing software
- Slope factor — multiply this by your roof footprint to get true surface area
Why pitch matters
Roof pitch determines almost every other roofing decision:
- Material choice — asphalt shingles below 2/12 won’t shed water, slate needs 4/12+, metal works on almost any pitch
- Cost — steeper roofs use more material (longer rafters, more surface area) and cost more in labor (harder to walk on, more safety setup)
- Walkability — pitches up to 6/12 are walkable; 7/12+ requires roof jacks or harnesses
- Drainage and snow shedding — steeper sheds water/snow faster, less ice damming risk
- Ventilation — attic volume scales with pitch, affecting ventilation requirements
Standard pitches by roof style
| Style | Typical pitch | Angle |
|---|---|---|
| Flat / low-slope | 0/12 to 2/12 | 0–9.5° |
| Shed / modern | 2/12 to 4/12 | 9.5–18.4° |
| Standard residential | 4/12 to 9/12 | 18.4–36.9° |
| Steep / colonial | 9/12 to 12/12 | 36.9–45° |
| Mansard / Victorian | 12/12+ | 45°+ |
| Gothic / steeple | 18/12 to 24/12 | 56–63° |
The formulas
Pitch from rise/run:
Pitch (X/12) = (rise / run) × 12
Angle = arctan(rise / run)Pitch from angle:
Rise/run ratio = tan(angle)
Pitch (X/12) = tan(angle) × 12Slope factor (the multiplier you need for surface area):
Slope factor = √(1 + (rise/run)²)For a 12/12 pitch (45°), the slope factor is √2 ≈ 1.414 — meaning a roof footprint of 1,000 sq ft has a true roof surface of 1,414 sq ft. Always factor pitch into roofing material orders.
Common pitch reference table
| Pitch | Rise/Run | Angle | Slope Factor |
|---|---|---|---|
| 2/12 | 0.167 | 9.46° | 1.014 |
| 3/12 | 0.250 | 14.04° | 1.031 |
| 4/12 | 0.333 | 18.43° | 1.054 |
| 5/12 | 0.417 | 22.62° | 1.083 |
| 6/12 | 0.500 | 26.57° | 1.118 |
| 7/12 | 0.583 | 30.26° | 1.158 |
| 8/12 | 0.667 | 33.69° | 1.202 |
| 9/12 | 0.750 | 36.87° | 1.250 |
| 10/12 | 0.833 | 39.81° | 1.302 |
| 12/12 | 1.000 | 45.00° | 1.414 |
Frequently asked questions
What is a 6/12 roof pitch?
A 6/12 roof pitch means the roof rises 6 inches for every 12 inches of horizontal run. As an angle, it's 26.57° from horizontal. It's the most common residential pitch in the US — steep enough to shed water and snow, shallow enough to walk on.
How do I measure roof pitch from the ground?
Hold a 12-inch level horizontally against the gable end of your roof, then measure the vertical distance from the end of the level to the roof surface. That measurement (in inches) is the rise per 12-inch run, giving you the X/12 pitch directly.
Is roof pitch the same as roof slope?
Roofers typically use 'pitch' to mean rise-over-run (X/12 ratio), and 'slope' to mean the angle in degrees. The terms are often used interchangeably in casual conversation, but inspectors and contractors use the X/12 format on permits and quotes.
What's the minimum roof pitch for shingles?
Asphalt shingles require a minimum 2/12 pitch (about 9.5°). Below that, water can get under shingle edges. For 2/12 to 4/12, you need an underlayment of 2 layers or ice-and-water shield. Standard shingle install (with one layer of underlayment) starts at 4/12.
How do I find the slope factor for surface area?
Slope factor = √(1 + (rise/run)²). For a 6/12 pitch, that's √(1.25) = 1.118. Multiply your roof footprint by this factor to get true surface area. The calculator returns this number in the third result box.