Roof Pitch Calculator
Convert rise and run or an angle into roof pitch (x/12), degrees, percent slope and the pitch factor — plus ridge height and rafter length.
Your estimate
6/12
Roof pitch
- Angle
- 26.57°
- Slope (grade)
- 50%
- Pitch factor (area multiplier)
- 1.12
- Roof type
- Conventional (walkable with care)
- Ridge height above wall plate
- 6 ft (72 in)
- Common rafter length (line length)
- 13.42 ft (161 in)
Show the math
- Pitch = 12 × rise ÷ run = 12 × 0.15 ÷ 0.3 = 6 in 12 (≈ 6/12)
- Angle = arctan(pitch ÷ 12) = 26.57°; grade = pitch ÷ 12 × 100 = 50%
- Pitch factor = √(1 + (pitch ÷ 12)²) = 1.12 — multiply plan area by this to get roof area
- Ridge height = (span ÷ 2) × pitch ÷ 12 = 6 ft (72 in); rafter = (span ÷ 2 + overhang) × factor = 13.42 ft (161 in)
Shopping list & cost
No materials list for this calculator — use the result in a materials calculator below.
Prices are what you enter under Advanced options. Estimates only — check stock and pricing with your supplier.
Quick answer A roof that rises 6 in over 12 in of run is a 6/12 pitch — 26.57°, a 50% slope, with a pitch factor of 1.12. On a 24 ft span the ridge sits 6 ft above the wall plates and each common rafter is 13.42 ft long before overhang. Metric: 15 cm rise over 30 cm is the same pitch (26.57°). Pitch = 12 × rise ÷ run; angle = arctan(rise ÷ run).
Method & assumptions
Pitch = 12 × Rise ÷ Run (written x/12) Angle = arctan(Rise ÷ Run) Slope % = Rise ÷ Run × 100 Pitch factor = √(1 + (Pitch ÷ 12)²) Rafter = (Span ÷ 2 + Overhang) × Pitch factor; Ridge height = Span ÷ 2 × Pitch ÷ 12
- Rise
- vertical distance
- Run
- horizontal distance (12 in for US pitch)
- Span
- outside-to-outside width of the walls under a gable
Assumptions & limits
- Rafter length is the line length to the ridge center; deduct half the ridge board thickness and add the tail for overhang when cutting.
- Symmetrical gable: both sides have the same pitch.
- Slope categories follow the IRC: shingles from 2/12, double underlayment below 4/12.
Rounding: purchase quantities are always rounded up to whole units as sold. See our methodology.
Diagram
How to use this calculator
- Choose whether you know the rise and run or the angle.
- To measure, hold a level horizontally against the underside of a rafter (or on the roof), mark 12 in along it and measure straight up to the roof — that is the rise.
- In metric, measure the rise over any run (30 cm or 1 m) — the calculator scales it to x/12.
- Optionally enter the building span to get the ridge height and common rafter length.
- Use the pitch factor in the roofing calculator to turn plan area into roof area.
Worked examples
Imperial: rise of 4½ in over 12 in
- Pitch = 4.5/12; angle = arctan(0.375) = 20.56°
- Slope = 37.5%; pitch factor = √(1 + 0.375²) = 1.068
Metric: roof angle 35°, span 8 m
- Pitch = 12 × tan 35° = 8.40/12 (70% slope)
- Ridge height = 4 × 0.70 = 2.80 m; rafter = 4 × 1.221 = 4.88 m
In depth: roof pitch planning notes
Pitch, angle and slope are three ways to say the same thing
In the US, roof pitch is written as rise over a 12 in run — 6/12 means the roof climbs 6 in for every foot it travels horizontally. Carpenters use this form because it maps directly onto a framing square. Elsewhere, and on most phone apps, slope is given as an angle in degrees or as a percentage, the rise divided by the run. All three describe the same triangle: 6/12 is 26.57° and 50%, 12/12 is 45° and 100%. This calculator converts between them so you can compare a pitch on the plans with an angle measured on site.
The pitch factor — the length of the sloped side for every unit of run — is what turns a flat footprint into roof area. It grows slowly at first and then quickly: 4/12 adds about 5%, 6/12 about 12%, 8/12 about 20% and 12/12 about 41%. That is why steep roofs need noticeably more shingles, underlayment and labor than their footprint suggests.
Rafters, ridge height and roofing limits
For a simple gable, half the building span is the run of each common rafter. Multiply it by the pitch factor for the rafter's line length to the center of the ridge, then subtract half the ridge board thickness and add the tail for any overhang when you cut it. The ridge height above the wall plate is simply half the span times the pitch ÷ 12 — a 24 ft span at 6/12 rises 6 ft. Rafter size and spacing are structural and come from the span tables in your code or the American Wood Council.
Pitch also decides which roofing you can use. Under the IRC, asphalt shingles need at least 2/12, and between 2/12 and 4/12 they need two layers of underlayment; below 2/12 you need a low-slope system such as a membrane. Metal panels and other products have their own minimums in the manufacturer's instructions. Above about 7/12 or 8/12, roofers usually need roof jacks and harnesses, and many price a steep-slope premium.
Reference table
| Pitch | Angle · pitch factor |
|---|---|
| 3/12 | 14.04° · 1.031 |
| 4/12 | 18.43° · 1.054 |
| 5/12 | 22.62° · 1.083 |
| 6/12 | 26.57° · 1.118 |
| 7/12 | 30.26° · 1.158 |
| 8/12 | 33.69° · 1.202 |
| 9/12 | 36.87° · 1.250 |
| 10/12 | 39.81° · 1.302 |
| 12/12 | 45.00° · 1.414 |
Key facts
- Most common US house pitch
- 4/12 to 9/12
- Asphalt shingles minimum
- 2/12 (IRC R905.2.2)
- 12/12
- 45°, 100% slope
Tips & common mistakes
- Measure pitch from the attic on a rafter rather than on the roof — it is safer and more accurate.
- Phone level apps read angle; convert with this calculator rather than guessing the x/12 value.
- For roofing quotes, the pitch also changes labor: above about 7/12 to 8/12 roofers often charge a steep-slope premium.
Frequently asked questions
What angle is a 6/12 roof pitch?
26.57°. A 6/12 roof rises 6 in for every 12 in of horizontal run, a 50% slope.
How do I find the pitch of my roof?
Hold a level horizontally, measure 12 in along it from the roof surface or rafter, then measure vertically up to the roof. The number of inches is the pitch over 12.
What is the minimum pitch for shingles?
2/12 under the IRC. Between 2/12 and 4/12, shingles need two layers of underlayment.
What is a 4/12 pitch in degrees?
18.43°, a 33.3% slope, with a pitch factor of 1.054.
What is the pitch factor used for?
Multiply the flat plan area (the footprint) by the pitch factor to get the actual sloped roof area.
Sources
- Seattle Residential Code 2018 (IRC-based), Chapter 9 Roof Assemblies (PDF) — accessed : “R905.2.2 Slope. Asphalt shingles shall be used only on roof slopes of two units vertical in 12 units horizontal (17-percent slope) or greater. For roof slopes from two units vertical in 12 units horizontal (17-percent slope) up to four units vertical in 12 units horizontal (33-percent slope), double underlayment application is required”
- NIST SP 811, Appendix B.9 – conversion factors — accessed : “foot (ft) → meter (m): 3.048 E−01; inch (in) → meter (m): 2.54 E−02”
- American Wood Council – span tables for joists and rafters — general reference — not cited for a specific figure
Default values (yields, coverage rates and densities) are typical figures from manufacturer literature. Always check the label on the product you buy.
Related calculators
- Roofing CalculatorRoof area from building size, overhang and pitch for gable, hip or shed roofs — squares, shingles, underlayment, drip edge, ice shield and ridge cap.
- Shingle CalculatorTurn a house footprint and roof pitch into roof area, roofing squares and shingle bundles, plus starter, ridge cap and underlayment.
- Siding CalculatorSiding squares for a house — walls plus gables, minus doors and windows — with vinyl boxes or fiber cement planks, J-channel, corners and starter.
Learn more in our guides
Method, waste and worked examples: Roof area, squares and waste.
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DIYCalcLab. “Roof Pitch Calculator.” Oct 19, 2026. https://diycalclab.com/roofing/roof-pitch-calculator/
Estimates only. Verify quantities with your supplier and local building codes. For structural, electrical or safety-critical work, consult a licensed professional. Full disclaimer.