Roof Pitch & Angle Calculator
Use this roof pitch calculator to convert pitch to degrees, percent slope, pitch multiplier, and rafter length. It also works as a shed roof pitch calculator and lean-to roof pitch calculator for single-slope roofs.
Quick answer: Roof pitch is written as rise over 12 inches of run. A 6/12 roof rises 6 inches for every 12 inches of horizontal distance. This page helps you calculate roof pitch, roof angle in degrees, slope factor, and rafter length in one place.
What is roof pitch?
Roof pitch is the ratio of vertical rise to horizontal run, usually written as X/12. A 4/12 pitch rises 4 inches in 12 inches of run, while a 10/12 pitch rises 10 inches in the same distance. Roof slope, roof angle, and pitch all describe how steep a roof is, but contractors usually talk in pitch while engineers and homeowners may think in degrees or percent slope.
Why pitch matters for materials
A roof with more pitch has more actual surface area than its flat footprint. That matters when ordering shingles, underlayment, fasteners, and metal panels. The pitch multiplier, also called a slope factor, helps convert plan area into real roof area so you do not under-order material on steep roofs.
Measuring pitch on the job
Use a level and tape measure. Hold the level perfectly horizontal against a rafter or roof surface, measure 12 inches along the level, then measure vertically from that point up to the roof. That vertical dimension is the rise. If it measures 6 inches, the roof pitch is 6/12.
Shed / lean-to roof pitch
This calculator also works as a shed roof pitch calculator or lean-to roof pitch calculator. For a shed roof, use the full horizontal run of the single sloped roof plane instead of half the building span. The same roof pitch to degrees conversion and slope factor still apply.
How to calculate roof pitch
- Measure the rise. This is the vertical height change.
- Measure the run. Standard pitch format uses 12 inches of run, but the calculator can use any run when solving from real measurements.
- Convert to X/12 pitch. Divide rise by run, then multiply by 12.
- Convert to degrees if needed. This is useful for metal roofing details, flashing layouts, and framing checks.
- Use the multiplier for area. Multiply footprint area by the pitch multiplier to estimate actual roof surface area.
Common roof pitch examples
4/12: common moderate residential slope.
6/12: very common for asphalt shingle roofs.
8/12: steeper look, more roof area, more care needed during installation.
12/12: rises 45 degrees and is considered very steep.
Pitch, angle, and percent slope
These are different ways to describe the same roof geometry. Pitch is contractor-friendly, degrees are useful for layout and cutting, and percent slope is common in some estimating and technical contexts. A good roof slope calculator should let you move between all three without guessing.
When to use rafter length
Rafter length helps with framing takeoffs, cuts, and rough material planning. It is especially helpful when laying out shed roofs, lean-to roofs, porches, patio covers, and small additions where rise and run are already known.
Roof pitch formulas
Pitch from rise and run
pitch = (rise ÷ run) × 12
Degrees from pitch
degrees = arctan(pitch ÷ 12)
Pitch multiplier
√(1 + (pitch ÷ 12)²)
Percent slope
(pitch ÷ 12) × 100
Frequently asked questions
Is roof pitch the same as roof angle?
Not exactly. Roof pitch is usually written as rise over 12, such as 6/12. Roof angle is the same slope expressed in degrees. They describe the same roof, but in different formats.
How do I convert roof pitch to degrees?
Use the rise-over-run relationship. This calculator does it automatically, which is faster and avoids mistakes when working with uncommon pitches like 2.5/12 or 7.25/12.
Can I use this for a shed roof or lean-to roof?
Yes. Select shed / lean-to roof and use the full run of the single roof plane. That makes it useful for patio covers, porches, sheds, and simple additions.
What is a pitch multiplier used for?
It converts flat plan area into actual sloped roof area. Estimators use it to figure shingle, underlayment, metal panel, and labor quantities more accurately.