Roof Pitch Reference Chart
| Pitch | Degrees | Slope % | Area multiplier | Classification | Typical materials |
|---|---|---|---|---|---|
| 1/12 | 4.76° | 8.3% | 1.003 | Low slope | Membrane (TPO/EPDM), built-up roofing |
| 2/12 | 9.46° | 16.7% | 1.014 | Low slope | Membrane, or shingles with double underlayment |
| 3/12 | 14.04° | 25% | 1.031 | Low slope (shingle minimum) | Asphalt shingles (min. pitch), membrane |
| 4/12 | 18.43° | 33.3% | 1.054 | Conventional | Asphalt, metal, tile |
| 5/12 | 22.62° | 41.7% | 1.083 | Conventional | Asphalt, metal, tile |
| 6/12 | 26.57° | 50% | 1.118 | Conventional | Asphalt, metal, tile, wood shake |
| 7/12 | 30.26° | 58.3% | 1.158 | Conventional | Asphalt, metal, slate |
| 8/12 | 33.69° | 66.7% | 1.202 | Conventional (upper limit) | Most materials |
| 9/12 | 36.87° | 75% | 1.250 | Steep slope | Most materials, fall protection recommended |
| 10/12 | 39.81° | 83.3% | 1.302 | Steep slope | Metal, slate, tile — fall protection required |
| 11/12 | 42.51° | 91.7% | 1.357 | Steep slope | Metal, slate, tile — fall protection required |
| 12/12 | 45.00° | 100% | 1.414 | Steep slope | Metal, slate, tile — fall protection required |
Pitches above 12/12 exist mostly on architectural features (turrets, steep gables, A-frame cabins) rather than full roof planes. The nearest-standard-pitch snap in the calculator uses this same chart.
How to Measure Roof Pitch
- Hold a carpenter's level against the roof surface or the underside of a rafter so it sits truly horizontal.
- From one end of the level, measure 12 inches along it (the run) and mark that point.
- Measure straight down (plumb) from that mark to the roof or rafter — that distance in inches is the rise.
- Write the pitch as rise over 12 (a 6-inch rise is 6/12). Enter the numbers above for degrees, slope percent, and area multiplier.
To stay off the roof, do the same from inside the attic against the underside of a rafter.
How to Calculate Roof Pitch
Pitch ratio = (rise ÷ run) × 12. Slope angle = arctan(rise ÷ run). Area multiplier = √(rise² + run²) ÷ run. Rafter length (before overhang) = horizontal span × area multiplier. Roof area (simple gable, approx.) = building width × span × area multiplier.
Worked example: rise = 6", run = 12". Pitch = (6 ÷ 12) × 12 = 6/12. Angle = arctan(6/12) = 26.57°. Area multiplier = √(6² + 12²) ÷ 12 = 1.118. If horizontal span = 15 ft, rafter length = 15 × 1.118 = 16.77 ft before overhang.
Pitch by Roof Type
Low-slope (about 1/12–3/12) is membrane or special shingle details. Conventional (4/12–8/12) covers most asphalt, metal, and tile houses, with 6/12 especially common in the US. Steep slope (9/12 and up) needs fall protection and extra fastening; 12/12 is a 45° A-frame. Shed and lean-to use the same math on a single plane — often a bit steeper than you’d guess from the short span, so water still leaves the wall.
USA vs UK Roof Pitch Conventions
The US writes pitch as inches of rise per 12 inches of run. The UK quotes the angle in degrees and measures in millimetres and metres. A UK roof at 40° converts to roughly a 10/12 US pitch — use Degrees ↔ Pitch with the UK toggle to confirm. 35–50° is typical for UK tiled roofs; 4/12–9/12 is the usual US housing band.
Why Roof Pitch Matters
- Material quantity — multiply footprint by the area multiplier (plus a 10–15% waste factor) before ordering shingles, underlayment, or metal panels.
- Labor and safety — pitches above roughly 9/12 (37°) require fall-protection equipment and slow crews down.
- Material compatibility — roofs below 3/12 can't use standard asphalt shingles without a waterproof membrane; steep roofs over 9/12 need extra fasteners and may exclude heavier materials like clay tile.
- Drainage and snow shedding — steeper pitches shed water and snow faster.
- Solar panel planning — panel output and racking design depend directly on slope angle.
Frequently Asked Questions
What is roof pitch and how is it measured?
Roof pitch is the steepness of a roof, usually written as inches of vertical rise per 12 inches of horizontal run (e.g., 6/12). Measure it by holding a level against the roof or a rafter, marking 12 inches along it, then measuring straight down to find the rise.
How do I calculate roof pitch from rise and run?
Divide the rise by the run, then multiply by 12 to express it as an x/12 ratio. For example, a 6-inch rise over a 12-inch run gives a 6/12 pitch. Enter both numbers into the calculator above for an instant result plus the angle and area multiplier.
What is roof pitch in degrees versus the x/12 ratio?
The x/12 ratio and degree measurement describe the same slope in two different units. The ratio compares rise to a fixed 12-inch run; the degree value is the angle formed between the roof and a horizontal line. A 6/12 pitch equals 26.57°; a 12/12 pitch equals exactly 45°.
What is the most common roof pitch in the USA? In the UK?
Most US homes fall between 4/12 and 9/12, with 6/12 especially common. Most UK homes are pitched between 35° and 50°, with 40–45° typical on traditional tiled roofs.
What is a 4/12, 6/12, and 8/12 pitch in degrees?
A 4/12 pitch is 18.43°, a 6/12 pitch is 26.57°, and an 8/12 pitch is 33.69°. See the full reference chart above for every pitch from 1/12 to 12/12.
How do I measure roof pitch without going on the roof?
Measure from inside the attic instead. Hold a level flat against the underside of a rafter, mark 12 inches along it, and measure straight down from that mark to the rafter's surface — that distance in inches is your rise.
How do I calculate a shed or lean-to roof pitch?
The math is identical to a standard roof — rise divided by run, multiplied by 12. Use the Shed/Lean-To mode above, which also flags that attached shed roofs are commonly built steeper (relative to their shorter span) to maintain adequate drainage.
How does pitch affect how much roofing material I need?
A steeper roof has more actual surface area than the building's footprint. Multiply your footprint by the pitch's area multiplier, then add a 10–15% waste factor, to estimate the roofing squares you need to order.
What roof pitch is walkable versus considered steep?
Pitches up to about 6/12 (26.57°) are generally walkable without special gear. From 7/12 to 9/12, caution is advised. Above roughly 9/12 (37°), most contractors require fall-protection equipment.
What is the minimum pitch for asphalt shingles, metal, or a flat roof membrane?
Standard asphalt shingles typically need a minimum of 2/12 to 3/12, often with an added waterproof underlayment layer at the low end. Below 2/12, a membrane system (TPO, EPDM, or modified bitumen) is required instead of shingles. Metal roofing can generally go as low as 3/12.
How do I convert roof pitch to a percentage or degrees and back?
Slope percentage is (rise ÷ run) × 100. Degrees is arctan(rise ÷ run). To go from degrees back to a ratio, take the tangent of the angle and multiply by 12. The Degrees ↔ Pitch mode above converts both directions automatically.
What's the difference between UK and US roof pitch conventions?
The US expresses pitch as a rise-over-12 ratio using imperial units; the UK expresses it as an angle in degrees using metric measurements. The two describe the same physical slope — use the unit toggle above to switch between them instantly.