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Roof Pitch Calculator

Free roof pitch calculator. Calculate roof slope in degrees, X/12 ratio, and percentage. Find rafter length from rise and run measurements.

1,000+ Contractors Reviewed by Pros By EstimationPro Team
Calculation Mode
in
in
ft

Pitch Visualization

RunRise26.6°

Roof Pitch Results

Pitch Ratio

6.0:12

Angle

26.6°

Percentage

50.0%

Category

Moderate

Rafter Calculation

Horizontal Run15.0 ft
Rafter Length16.77 ft
Pitch Multiplier1.118

12,800+ estimates calculated this month

Common Pitch Reference

PitchDegreesTypical Use
1:124.8°Flat roofs, low-slope commercial
2:129.5°Low-slope, requires special materials
3:1214.0°Minimum for standard shingles
4:1218.4°Common residential, easy to walk
5:1222.6°Common residential
6:1226.6°Most popular residential pitch
7:1230.3°Steeper residential
8:1233.7°Steep, good for snow shedding
9:1236.9°Very steep, harder to walk
10:1239.8°Very steep, needs scaffolding
12:1245.0°Maximum common pitch (45°)

Roof Pitch Reference Guide

Pitch measurement, angle conversions, and area multipliers for roof calculations.

What Is Roof Pitch and How Is It Measured?

Roof pitch is expressed as rise over run — for example, 6/12 means the roof rises 6 inches for every 12 inches of horizontal distance.

  • Low slope: 2/12 to 4/12 (nearly flat, requires special roofing)
  • Standard: 4/12 to 9/12 (most residential homes)
  • Steep: 9/12 to 12/12 (dramatic look, sheds water/snow quickly)
  • Very steep: 12/12+ (45°+, specialized installation required)

To measure pitch: place a level horizontally at the roof edge, measure 12" out, then measure the vertical rise from that point to the roof surface. The rise in inches is your pitch.

Key Takeaways

  • Pitch = rise ÷ 12 inches of run
  • Standard residential: 4/12 to 9/12
  • 6/12 is the most common US residential pitch

Roof Pitch to Angle Conversion

Converting pitch to degrees uses the formula: angle = arctan(rise/12). Here are common conversions:

  • 2/12: 9.5°
  • 4/12: 18.4°
  • 6/12: 26.6°
  • 8/12: 33.7°
  • 10/12: 39.8°
  • 12/12: 45.0°

Building codes typically define "steep slope" as anything above 3/12 (14°) and "low slope" below that. Low-slope roofs require built-up, modified bitumen, or single-ply membrane roofing.

Key Takeaways

  • 6/12 pitch = 26.6 degrees
  • 12/12 pitch = 45 degrees
  • Below 3/12 requires special membrane roofing

Pitch Multiplier for Roof Area Calculation

Multiply the flat (footprint) area by the pitch factor to get actual roof area. Steeper pitches mean significantly more material.

  • 4/12 pitch: multiply footprint × 1.054
  • 6/12 pitch: multiply footprint × 1.118
  • 8/12 pitch: multiply footprint × 1.202
  • 10/12 pitch: multiply footprint × 1.302
  • 12/12 pitch: multiply footprint × 1.414

Example: A home with a 1,500 sq ft footprint and 8/12 pitch has 1,500 × 1.202 = 1,803 sq ft of actual roof area (18 roofing squares).

Key Takeaways

  • 6/12 pitch factor: 1.118 (12% more area)
  • 12/12 pitch factor: 1.414 (41% more area)
  • Multiply footprint × pitch factor for true area

How to Use This Calculator

Choose your input mode

Select "Rise & Run" if you have measured the vertical rise and horizontal run, or "Known Pitch" if you already know the pitch as an X:12 ratio.

Enter your measurements

For Rise & Run mode, enter the rise and run in inches. For Known Pitch mode, enter the pitch value (e.g., 6 for a 6:12 pitch).

Enter the rafter run

Input the horizontal rafter run in feet to calculate the actual rafter length needed for your roof.

Review results and reference table

See your pitch expressed as a ratio, angle, and percentage, plus the visual pitch indicator and common pitches reference table.

Roof Pitch Formulas

Pitch Ratio = (Rise / Run) x 12 → expressed as X:12
Angle (degrees) = arctan(Rise / Run) x (180 / pi)
Percentage = (Rise / Run) x 100
Rafter Length = Run / cos(Angle)
Pitch Multiplier = 1 / cos(Angle)

Where:

Rise
= Vertical distance in inches
Run
= Horizontal distance in inches
Pitch Multiplier
= Multiply flat area by this to get actual roof area

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Frequently Asked Questions

What does roof pitch mean?
Roof pitch describes the steepness of a roof as a ratio of vertical rise to horizontal run. A 6:12 pitch means the roof rises 6 inches for every 12 inches of horizontal run. Pitch is commonly expressed as X:12, in degrees, or as a percentage.
What is the most common roof pitch?
The most common residential roof pitch is 4:12 to 6:12. A 6:12 pitch (26.6 degrees) is the most popular because it sheds water and snow effectively while remaining easy to walk on for maintenance.
What is the minimum pitch for shingles?
Standard asphalt shingles require a minimum pitch of 3:12 (14 degrees). Below that, you need special low-slope roofing materials like modified bitumen, TPO, or built-up roofing. Some shingle manufacturers allow 2:12 with additional underlayment.
How do I measure roof pitch from inside the attic?
Place a level horizontally against a rafter and measure 12 inches from the point where the level meets the rafter. Then measure the vertical distance from the end of the level down to the rafter. That vertical measurement is your pitch as X:12.
How does pitch affect roofing cost?
Steeper roofs cost more to install because they require additional safety equipment, take longer to work on, and use more materials. A pitch multiplier is applied to the flat roof area: for example, a 6:12 pitch has a multiplier of about 1.118, meaning 11.8% more material than the flat footprint.

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