Roof Slope Calculator
Instantly calculate roof pitch, angle, slope percentage, and rafter length with real-time interactive visualization. Free, fast — no ads, no sign-ups.
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Common Roof Pitch Reference Chart
A complete reference for the 12 most common roof pitches in the US standard (rise per 12 inches of run). Click any row to load it into the calculator above.
| Pitch | Angle | Slope % | Multiplier | Category | Action |
|---|---|---|---|---|---|
| 1 : 12 | 4.8° | 8.3% | 1.003 | Flat Roof | |
| 2 : 12 | 9.5° | 16.7% | 1.014 | Flat Roof | |
| 3 : 12 | 14.0° | 25.0% | 1.031 | Low Slope | |
| 4 : 12 | 18.4° | 33.3% | 1.054 | Low Slope | |
| 5 : 12 | 22.6° | 41.7% | 1.083 | Standard | |
| 6 : 12 | 26.6° | 50.0% | 1.118 | Standard | |
| 7 : 12 | 30.3° | 58.3% | 1.158 | Standard | |
| 8 : 12 | 33.7° | 66.7% | 1.202 | Standard | |
| 9 : 12 | 36.9° | 75.0% | 1.250 | Standard | |
| 10 : 12 | 39.8° | 83.3% | 1.302 | Steep | |
| 11 : 12 | 42.5° | 91.7% | 1.357 | Steep | |
| 12 : 12 | 45.0° | 100.0% | 1.414 | Steep |
How to Measure Roof Pitch
There are three common ways to determine your roof's pitch. Choose the method that works best for your situation — no contractor required.
Method 1
From the Attic
The most accurate method — measure directly from the underside of the roof rafters.
- 1Place a level horizontally against the bottom of a rafter.
- 2Measure 12 inches along the level from the point where it touches the rafter.
- 3From the 12-inch mark, measure vertically up to the underside of the rafter.
- 4This vertical measurement is your rise. Your pitch is rise : 12.
Method 2
From the Roof Surface
Measure directly on the roof — useful during inspections or repairs.
- 1Place a level on the roof surface so it sits horizontally.
- 2Measure 12 inches along the level.
- 3From the 12-inch mark, measure perpendicular to the level down to the roof surface.
- 4That distance is your rise.
Method 3
From the Ground (Phone Method)
Estimate your roof pitch without climbing — great for a quick check.
- 1Stand back far enough to see the full roof profile from the side.
- 2Open a free inclinometer app on your phone (search "clinometer" or "angle finder").
- 3Hold your phone edge-on and align it visually with the roof line.
- 4The app will read the angle in degrees — enter it above to find the pitch.
Understanding Roof Pitch vs Slope vs Angle
These three terms are often used interchangeably, but they describe the steepness of a roof differently. Here's how they relate to each other.
Pitch (Ratio)
Expressed as X : 12, where X is the vertical rise for every 12 horizontal inches of run. This is the US construction industry standard.
Example: A roof that rises 6 inches for every 12 inches of run has a 6:12 pitch.
Slope (Percentage)
The ratio of rise to run, expressed as a percentage. Commonly used in Europe, civil engineering, and road grading.
Example: A 6:12 pitch = 50% slope. A 45° angle = 100% slope.
Angle (Degrees)
The geometric angle between the roof surface and the horizontal plane, measured in degrees. Used universally in mathematics and architecture.
Example: A 6:12 pitch ≈ 26.57°. A 12:12 pitch = 45°.
Why Does the US Use X:12?
The X:12 system (also called "rise-in-12") originated because framing squares — the primary layout tool for carpenters — are marked in 12-inch increments. This makes it easy to mark rafter cuts directly: set the framing square to the pitch ratio and draw the cut line. Internationally, degrees and percentages are more common because they align with metric measurement systems and engineering standards.
What Roof Pitch Is Best? A Material & Climate Guide
Your roof pitch directly determines which materials you can use, how well it handles weather, and how much it costs. Here's a breakdown by slope range.
Materials
- Built-Up Roofing (BUR)
- TPO / EPDM membrane
- Modified bitumen
Climate Factors
- Requires excellent waterproofing
- Not suitable for heavy snow regions
- Good for arid / desert climates
Common Uses
- Commercial buildings
- Modern residential
- Rooftop decks / gardens
Materials
- Standing seam metal
- Corrugated metal panels
- Asphalt shingles (with underlayment)
Climate Factors
- Adequate drainage for moderate rain
- Ice dam risk in cold climates
- Good wind resistance
Common Uses
- Sheds and garages
- Porches / lean-tos
- Ranch-style homes
Materials
- Asphalt shingles (most popular)
- Wood shakes / shingles
- Metal roofing (any type)
- Clay / concrete tile
Climate Factors
- Excellent water shedding
- Good snow load management
- Works in all US climate zones
Common Uses
- Most residential homes
- Gable and hip roofs
- Multi-story buildings
Materials
- Slate (premium / longest lifespan)
- Wood shakes
- Architectural shingles
- Metal panels
Climate Factors
- Best for heavy snow (slides off)
- Excellent drainage
- Higher wind uplift risk
Common Uses
- Colonial / Cape Cod homes
- A-frame cabins
- Mountain / alpine buildings
Common Roof Pitch Scenarios
Not sure what pitch you need? Here are the most common building types and their typical roof pitches. Click "Try This" to load the values into the calculator.
Garage / Workshop
Typical pitch: 3 : 12
Most detached garages use a 3:12 to 4:12 pitch — enough slope for drainage while keeping the structure low-profile and affordable.
Works well in moderate climates. Add ice-and-water shield in cold regions.
Standard Residential Home
Typical pitch: 5 : 12
The 4:12 to 6:12 range is the sweet spot for most US homes — compatible with nearly all roofing materials and looks balanced from the curb.
Universal — handles rain, snow, and wind effectively.
Colonial / Cape Cod
Typical pitch: 9 : 12
Traditional Colonial homes feature steep 8:12 to 10:12 pitches. These create usable attic space and support premium materials like slate.
Excellent for heavy snow — snow slides off naturally.
A-Frame Cabin
Typical pitch: 12 : 12
A-frame structures use extreme 12:12 (45°) or steeper pitches. The roof IS the wall, maximizing snow shedding and creating a dramatic aesthetic.
Ideal for alpine / mountain locations with heavy snowfall.