Roof Pitch Calculator
Calculate roof pitch, slope angle, and rafter length from rise and run measurements.
Standard pitch format: X/12
Based on 26.6° slope angle
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What is Roof Pitch?
Roof pitch (or roof slope) describes how steep a roof is. It's expressed as a ratio of vertical rise to horizontal run - typically as "X/12" where X is the inches of rise for every 12 inches of horizontal run. A 6/12 pitch means the roof rises 6 inches for every foot of horizontal distance.
Knowing your roof pitch is essential for: selecting appropriate roofing materials (shingles require minimum slope), calculating rafter lengths for framing, estimating material quantities (steeper roofs have more surface area), and ensuring proper drainage.
Our calculator converts rise/run to degrees, calculates the rafter length multiplier, and recommends suitable roofing materials based on your slope.
Pitch Presets
9 common pitches from 1/12 (nearly flat) to 12/12 (45°). One-click selection for quick calculations.
Rafter Calculator
Enter building run to calculate exact rafter board length needed. No manual math required.
Material Guide
Automatic roofing material recommendations based on your calculated slope angle.
Visual Diagram
See your roof pitch visualized as a triangle diagram that updates in real-time.
How to Measure & Calculate Roof Pitch
Measure Rise
Place a 12" level on roof. At the 12" mark, measure vertical distance to roof surface. This is your rise.
Note the Run
Standard run is 12 inches. Your pitch is [Rise]/12. Example: 6" rise = 6/12 pitch.
Enter Values
Input rise and run in calculator. For building run (rafter calc), enter horizontal span from wall to ridge.
Get Results
View angle in degrees, grade %, rafter length, and material recommendations.
Roof Pitch Reference Chart
| Pitch | Angle | Multiplier | Category |
|---|---|---|---|
| 2/12 | 9.5° | 1.014 | Low Slope |
| 3/12 | 14.0° | 1.031 | Low Slope |
| 4/12 | 18.4° | 1.054 | Standard |
| 5/12 | 22.6° | 1.083 | Standard |
| 6/12 | 26.6° | 1.118 | Standard |
| 8/12 | 33.7° | 1.202 | Steep |
| 10/12 | 39.8° | 1.302 | Very Steep |
| 12/12 | 45.0° | 1.414 | Extreme |
Materials by Pitch
EPDM, TPO, PVC membrane, Built-up roofing
Metal panels, Modified bitumen, Special shingles with underlayment
Asphalt shingles, Clay/Concrete tiles, Slate, Wood shakes, Metal
Rafter Length Formula
Instead of using Pythagorean theorem for every rafter, use the multiplier:
Example: 15ft run × 1.118 (6/12 pitch) = 16.77ft rafter
* Add extra for overhangs, ridge cuts, and waste
Pro Tips for Roof Pitch
Measure from inside - Attic measurement is easier and safer than climbing on roof.
Check local codes - Some areas mandate minimum pitch for snow load or drainage.
Add 10% to rafters - Account for overhangs, ridge cuts, and cutting waste.
Steeper = more cost - Higher pitch means more surface area and labor.
Consider climate - Snow-prone areas benefit from 6/12+ pitch.
Use speed square - A rafter square has pitch markings for quick field checks.
Common Use Cases
Framing New Roof
Calculate rafter lengths before cutting lumber. Use multiplier for quick field math.
Roofing Estimates
Determine suitable materials and estimate surface area for material ordering.
Home Inspection
Verify roof pitch to assess drainage capability and material appropriateness.
Frequently Asked Questions
What is roof pitch?
Roof pitch is the slope of a roof expressed 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. It determines drainage capability and suitable roofing materials.
How do I measure roof pitch?
Place a level horizontally on the roof, mark 12 inches from one end, then measure vertically from that mark to the roof surface. This vertical measurement is your rise. A 6-inch rise over 12 inches run = 6/12 pitch. You can also measure from inside the attic.
What is the minimum pitch for shingles?
Standard asphalt shingles require minimum 4/12 pitch (18.4°). For 2/12 to 4/12 pitches, shingles can work but require additional underlayment and special installation. Below 2/12, use membrane roofing (TPO, EPDM, or built-up).
What is a rafter length multiplier?
The rafter multiplier is a factor used to calculate diagonal rafter length from horizontal run. Multiply building run by the multiplier to get rafter length. For 6/12 pitch, multiplier is 1.118 - so a 15ft run needs 16.77ft rafters.
What pitch is a 45-degree roof?
A 45-degree roof angle equals 12/12 pitch (100% grade). This is considered very steep and is common in A-frame houses, steep gables, and dormers. The rise equals the run - for every 12 inches horizontal, roof rises 12 inches.
Is a steeper roof better?
Steeper roofs shed water and snow faster, have longer material lifespan, and offer more attic space. However, they cost more (more materials, harder to work on) and may not suit all architectural styles. Most residential roofs are 4/12 to 9/12 - a balance of function and cost.
What roofing material works for low-slope roofs?
Low-slope roofs (0/12 to 3/12) require: EPDM rubber membrane, TPO/PVC membranes, built-up roofing (BUR), modified bitumen, or standing seam metal. These materials create a waterproof seal since water drains slowly on flat roofs.
How do I convert pitch to degrees?
Use formula: Angle = arctan(rise/run). For 6/12 pitch: arctan(6/12) = 26.57°. Our calculator does this automatically. Common conversions: 4/12 = 18.4°, 6/12 = 26.6°, 8/12 = 33.7°, 12/12 = 45°.
What is grade percentage for roofs?
Grade (%) = (Rise/Run) × 100. A 6/12 pitch = 50% grade - the roof rises 50% of the horizontal distance. Grade is used more in road engineering but helps compare roof steepness. 100% grade = 45°.
How much extra rafter length should I order?
Add extra for: eave overhang (typically 12-24 inches), ridge cut (1-2 inches), and cutting waste (5-10%). For a 15ft calculated rafter, order 18ft lumber. Always measure twice and factor in your soffit design.