Calculate roof pitch from rise and run — get angle in degrees, slope percentage, and ratio (e.g. 4:12)
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Enter a value above or select a common pitch
About This Tool
Roof pitch describes how steep a roof is. Builders express it as a ratio (like 4:12 — 4 inches of rise per 12 inches of run), but architects may use degrees, and engineers often use slope percentage. This calculator converts between all three formats instantly.
Enter any one value — rise and run, angle in degrees, or slope percentage — and the calculator fills in the rest. It also shows the rafter length factor (how much longer a rafter is compared to horizontal run), which is essential for estimating roofing materials.
Whether you're measuring an existing roof, designing a new one, or ordering materials, this tool eliminates the trigonometry and gives you every pitch format in one place.
How to Use
1. Choose your input mode: Rise & Run, Angle, or Slope %
2. Enter the known value(s)
3. Read all converted results: ratio, angle, slope %, and rafter factor
4. Use preset buttons for common pitches (4:12, 6:12, etc.)
5. Toggle between Imperial and Metric for rise/run values
6. Use "Copy Link" to save or share your calculation
A 4:12 pitch means the roof rises 4 inches for every 12 inches of horizontal run. That's an angle of about 18.4° and a slope of 33.3%. A 4:12 pitch is one of the most common residential roof pitches — steep enough for good water drainage but shallow enough to walk on safely.
What is the most common roof pitch?
The most common residential roof pitches are 4:12, 5:12, and 6:12. A 4:12 pitch (18.4°) is the minimum recommended for standard asphalt shingles. Steeper pitches like 8:12 or 12:12 are used for architectural style or heavy snow areas. Low-slope roofs (1:12 to 2:12) typically require membrane or built-up roofing.
How do I measure roof pitch?
Place a level horizontally against the roof (or in the attic against a rafter). Mark 12 inches along the level from the point where it touches the roof. Measure straight down from that mark to the roof surface — that vertical distance is the rise. Your pitch is rise:12. For example, if you measure 6 inches down, your pitch is 6:12.
What roof pitch is walkable?
Most people can comfortably walk on a roof with a pitch of 6:12 (26.6°) or less. Pitches between 7:12 and 9:12 require caution and roof jacks. Anything above 10:12 (39.8°) is considered steep and generally requires scaffolding or specialized equipment for safe access.
How do I convert roof pitch to degrees?
Divide the rise by the run and take the arctangent. For a 4:12 pitch: arctan(4/12) = arctan(0.333) = 18.43°. For a 6:12 pitch: arctan(6/12) = arctan(0.5) = 26.57°. This calculator does the conversion automatically.
What is the minimum roof pitch for shingles?
Standard asphalt shingles require a minimum pitch of 4:12 (18.4°). Some manufacturers allow 2:12 with special underlayment. Metal roofing can go as low as 1:12 (4.8°) with standing seam panels. Flat roofs (below 2:12) need membrane, built-up, or spray-applied roofing systems.
What is the rafter factor?
The rafter factor (also called the rafter length multiplier) tells you how long a rafter is relative to the horizontal run. For a 4:12 pitch, the factor is 1.054 — meaning a rafter spanning 10 feet of run is actually 10.54 feet long. It's calculated as √(1 + (rise/run)²). This is essential for ordering lumber and calculating roofing material area.