Roof pitch is just a ratio — vertical rise per 12 inches of horizontal run. This calculator turns any two measurements (run and rise in any unit) into the four numbers you actually need: pitch, angle, grade percent, and rafter length.
How pitch is calculated
angle = arctan(rise ÷ run) (in degrees)
grade = (rise ÷ run) × 100 (as percent)
The calculator converts everything to a common unit internally, so you can mix feet and inches without losing precision.
Standard roof pitches and what they’re used for
| Pitch | Angle | Use case |
|---|---|---|
| 1/12 | 4.76° | Commercial flat roofs, EPDM membrane only |
| 2/12 | 9.46° | Low-slope residential, requires special underlayment |
| 3/12 | 14.04° | Modern minimalist designs, tile risk territory |
| 4/12 | 18.43° | Most common residential pitch — works for any shingle |
| 5/12 | 22.62° | Common in mid-Atlantic / midwest residential |
| 6/12 | 26.57° | Common in northern US (sheds snow well) |
| 8/12 | 33.69° | Steep residential, full-walkable for installation |
| 9/12 | 36.87° | Steep — needs roof jacks, hard to walk |
| 12/12 | 45° | Very steep — dramatic, expensive to roof |
| 18/12 | 56.31° | Victorian / Gothic — specialty contractors only |
How pitch affects cost
Steeper roofs cost more — not just because of the math but because:
- More material: A 12/12 roof has 41% more surface area than a 4/12 roof of the same building footprint
- Slower installation: Anything over 8/12 typically requires roof jacks, scaffolding, or harnesses
- Safety premium: Roofing labor costs 25-50% more for pitches above 8/12
- Underlayment requirements: Below 4/12, code requires a double layer of underlayment
Adding pitch to an existing low-slope roof is one of the most expensive renovations in residential construction (usually $20K+ for a small house). Plan the pitch right the first time.
Reading pitch from existing construction
If you’re working on an existing roof and need to know the pitch:
- Inside the attic: Climb up with a 24" level and a tape measure. Hold the level against the bottom of a rafter, perfectly horizontal. Measure 12" out from where the level touches the rafter. Then measure the vertical distance from the level down to the rafter at that 12" mark — that’s your rise. Plug into the calculator.
- Outside on a flat roof section: Use a smartphone level app (iOS Compass app has one built in) held flat against the roof. Read the angle in degrees, then look it up in our chart above (or use the calculator backwards: rise = run × tan(angle)).
The attic method is more accurate. The phone method is faster but adds 1-2° of error.
Cathedral ceilings and pitch breaks
For homes with multiple roof sections at different pitches (common with additions or dormers), measure each section separately. The calculator gives you a single value — for whole-house framing or material orders, average the pitches weighted by surface area, or just calculate each section.
Frequently asked questions
What is roof pitch?
Roof pitch is the slope of a roof, expressed as inches of vertical rise per 12 inches of horizontal run. A 4/12 pitch (read "four in twelve") means the roof rises 4 inches for every 12 inches of horizontal distance. Steeper pitches shed water and snow faster but cost more to build.
What pitch is best for shingles?
Asphalt shingles work on pitches from 2/12 to 21/12. Standard residential pitches are 4/12 to 9/12. Below 2/12, you need a low-slope underlayment (or a different roofing material like rolled or membrane). Above 12/12, installation gets dangerous and typically requires roof jacks or scaffolding.
How do I measure my roof pitch?
Two ways: (1) From inside the attic: Hold a level horizontally against a rafter, mark 12" out, then measure vertically from the level to the rafter at that 12" mark — that's your rise. (2) From outside: Use a smartphone level app on a flat section of roof, then convert the angle to pitch using our chart.
What's the difference between pitch, slope, angle, and grade?
Pitch = X/12 (rise per 12 inches of run). Slope = same as pitch in roofing context. Angle = degrees from horizontal. Grade = percent (rise/run × 100). 4/12 pitch = 18.43° angle = 33.3% grade. Pitch is the standard in US framing; degrees and grade are used in engineering and architectural drawings.
Does the building width matter?
No — pitch is a ratio, not an absolute. A 24 ft building and a 60 ft building can both have a 6/12 pitch. What changes is the rafter length and ridge height. Use this calculator with run and rise from any portion of the roof — the pitch will be identical.