Convert roof pitch between rise & run, X:12 ratio, degrees and percent slope in one pass. Get rafter length, pitch multiplier, material compatibility, walkability rating and snow-load factor — the numbers that actually decide how a roof gets built.
- Rise & Run
- X:12 Pitch
- Degrees
- Percent Slope
- Rafter Length
- Material Check
- Walkability
A 6:12 roof rises 6 units for every 12 units of horizontal run. Enter 6. A 4:12 roof → enter 4.
A 6:12 roof is 26.57°. A 4:12 roof is 18.43°. UK/IE traditional pitches commonly sit at 40°–50°.
A 6:12 roof is 50%. Percent is rise ÷ run × 100 — it is not the angle. 100% slope is 45°.
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Choose an input mode and enter your pitch, then press Calculate Roof Pitch.
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Roofing material compatibility at this pitch
Roof Pitch Conversion Chart
The four ways a pitch is written, side by side. Use this when a supplier, code, or drawing uses a different format to yours.
| X:12 Pitch | Degrees | Grade % | Multiplier | Category |
|---|---|---|---|---|
| 1:12 | 4.76° | 8.33% | 1.003 | Very low — membrane only |
| 2:12 | 9.46° | 16.67% | 1.014 | Low — asphalt with special underlayment |
| 3:12 | 14.04° | 25.00% | 1.031 | Low — metal shingle minimum |
| 4:12 | 18.43° | 33.33% | 1.054 | Standard — most materials OK |
| 5:12 | 22.62° | 41.67% | 1.083 | Standard residential |
| 6:12 | 26.57° | 50.00% | 1.118 | Most common residential |
| 7:12 | 30.26° | 58.33% | 1.158 | Steep residential |
| 8:12 | 33.69° | 66.67% | 1.202 | Steep — roof jacks required |
| 9:12 | 36.87° | 75.00% | 1.250 | Very steep — harness required |
| 10:12 | 39.81° | 83.33% | 1.302 | Very steep — specialised work |
| 12:12 | 45.00° | 100.00% | 1.414 | Extreme — not standard residential |
How to Calculate Roof Pitch
Roof pitch is the ratio of vertical rise to horizontal run. Every other format — degrees, percent, multiplier — is derived from that single ratio.
Pitch Ratio (X:12)
Divide the rise by the run, then multiply by 12.
Pitch = (Rise ÷ Run) × 12
Angle in Degrees
Take the inverse tangent of the rise over run.
Angle = arctan(Rise ÷ Run)
Slope Percent
Multiply the ratio by 100. This is what site grading and drainage plans use.
Grade (%) = (Rise ÷ Run) × 100
Pitch Multiplier
The factor that converts plan (footprint) area to actual sloped roof area.
Multiplier = √(1 + (Rise ÷ Run)²)
A 6:12 pitch is 26.57°, not 50°. The 50 is the grade percent, not the degrees. Mixing these up in a material order or a code submission is the single most common pitch mistake on site. The relationship is Angle = arctan(Pitch ÷ 12).
Worked Pitch Examples from Site
| Task | Given | Calculation | Result |
|---|---|---|---|
| Standard house | Rise 6, Run 12 | (6 ÷ 12) × 12 | 6:12 = 26.57° = 50% |
| Low slope garage | Rise 3, Run 12 | (3 ÷ 12) × 12 | 3:12 = 14.04° = 25% |
| Steep roof | Rise 9, Run 12 | (9 ÷ 12) × 12 | 9:12 = 36.87° = 75% |
| UK traditional | Rise 45, Run 12 | arctan(45 ÷ 12) × 180 / π | ~75° — but typical is 40–50° |
| Roof area estimate | Plan 1500 ft², 6:12 pitch | 1500 × 1.118 | 1677 ft² actual roof surface |
| Rafter length | Run 12 ft, 6:12 pitch | 12 × 1.118 | 13.42 ft rafter length |
| Ridge height | Span 24 ft, 6:12 pitch | (24 ÷ 2) × 0.5 | 6 ft ridge height above wall plate |
| Material check | 2:12 pitch, asphalt shingles | Check NRCA minimum 2:12 | OK with double underlayment |
How to Measure Roof Pitch on Site
From the attic rafter
The most accurate method. Hold a level against the underside of a rafter. Mark 12 units along the level, then measure vertically up to the rafter. That vertical measurement is your rise.
From the ground with a level
On a gable end, hold a level against the rake edge. Mark 12 units along the level, then measure vertically to the roof surface. Works well on standard gable roofs.
From a photograph
On a clear elevation photo, draw a horizontal line and measure pixels for run, then pixels for rise. The ratio of pixels equals the actual pitch. Accuracy depends on a true elevation shot, not perspective.
With a digital pitch gauge
Place the gauge flat on the roof surface and read the angle directly. Most smartphone apps work as clinometers, but verify with a physical level on anything critical. A 1° error is roughly a 1 cm error over 60 cm of run.
Minimum Roof Pitch by Material
Below these pitches, the material will not shed water reliably. This table follows NRCA recommendations and IRC/IBC minimums.
| Material | Minimum pitch | Degrees | Notes |
|---|---|---|---|
| Low-slope membranes (flat roofs) | |||
| TPO / EPDM single-ply | 1/4:12 to 1:12 | 1.2°–4.8° | Suitable for flat to 1:12; heat-welded seams |
| Built-up roofing (BUR) | 1/4:12 to 1:12 | 1.2°–4.8° | Gravel or cap sheet surface |
| Modified bitumen | 1/4:12 to 1:12 | 1.2°–4.8° | Torch-applied or self-adhered |
| Steep-slope materials | |||
| Asphalt shingles (3-tab) | 2:12 | 9.5° | Double underlayment required between 2:12 and 4:12 |
| Asphalt shingles (architectural) | 2:12 | 9.5° | Same underlayment rule as 3-tab |
| Metal shingles / stamped panels | 3:12 | 14.0° | Lapped seams require adequate slope |
| Standing seam metal | 1:12 | 4.8° | Concealed fastener profiles can go lower |
| Clay / concrete tile | 4:12 | 18.4° | NRCA recommends 4:12 minimum |
| Slate | 4:12 | 18.4° | Below 4:12 needs special underlayment |
| Wood shakes / shingles | 4:12 | 18.4° | NRCA recommends 4:12 or more |
| Solar considerations | |||
| Solar panels (flush mount) | Any pitch | — | Output falls as tilt deviates from latitude optimum |
| Solar panels (optimal tilt) | Latitude-dependent | — | Best at tilt ≈ latitude; 6:12 in most of US gives 95%+ of optimal |
Roof Pitch Standards by Country
| Country / Region | Typical residential pitch | Key code / standard | Watch out for |
|---|---|---|---|
| United States | 4:12 to 9:12 (18°–37°) | IRC R905 / IBC Ch.15 | Asphalt shingles below 4:12 need double underlayment |
| United Kingdom | 40°–50° | BS 5534 | 45° historically avoided for structural reasons |
| Ireland | 40°–50° | I.S. 444 | Similar to UK practice |
| Canada | 4:12 to 8:12 | NBC of Canada | Snow load governs pitch selection in most provinces |
| Australia | 15°–35° | AS 2050 | Cyclonic regions require steeper pitches and stronger fixings |
| New Zealand | 15°–35° | NZS 3604 | Similar to Australia; wind zones matter |
| Germany / EU | 30°–45° | DIN 18531 / EN 1991-1-3 | Eurocode snow load maps dictate minimum |
| India | 15°–30° | IS 875 / NBC India | Monsoon drainage drives the lower bound |
| South Africa | 15°–30° | SANS 10400-L | Coastal areas need higher wind resistance |
| Gulf (UAE, KSA, Qatar) | 5°–15° | GSO / SASO | Shallow pitches common; sand and dust drainage must be considered |
| Japan | 20°–35° | JIS A 5402 | Seismic and snow loads both influence pitch |
To convert a pitch to a slope factor, add the pitch to 12, divide by 12, and adjust slightly. The exact method is Multiplier = √(1 + (Pitch ÷ 12)²). For a 6:12 roof: √(1 + 0.25) = √1.25 = 1.118. Multiply your plan area by 1.118 to get the actual surface area. A 2000 ft² footprint becomes 2236 ft² of roofing — and that is what you buy.
People Also Ask
What is a 6:12 roof pitch in degrees and percent?
A 6:12 roof pitch is 26.57° and 50% grade. It is the most common residential pitch in North America, rising 6 inches for every 12 inches of horizontal run.
What is a 4:12 roof pitch in degrees?
A 4:12 roof pitch is 18.43° and 33.33% grade. It is the minimum pitch for standard asphalt shingles without special underlayment in many jurisdictions.
How do I calculate rafter length from pitch?
Rafter length = Run × Pitch Multiplier. For a 6:12 pitch, the multiplier is 1.118. So a 12 ft run gives a 13.42 ft rafter. Always add the overhang separately — the rafter calculation gives the point-to-point distance from wall plate to ridge before any overhang is added.
What is the minimum roof pitch for asphalt shingles?
2:12 (9.5°) with a double layer of underlayment. Below 2:12, asphalt shingles are not permitted by most codes. The NRCA recommends 4:12 as the practical minimum for long-term performance. Below 4:12, the risk of wind-driven rain penetration increases significantly.
What is the minimum pitch for metal roofing?
Standing seam metal can go as low as 1:12 (4.8°) with concealed fasteners. Metal shingles and stamped panels typically require 3:12 (14°) because of their lapped seams. Always check the manufacturer's installation guide for the specific profile.
How do I convert roof pitch to degrees?
Use the formula: Degrees = arctan(Pitch ÷ 12). For a 6:12 pitch: arctan(6/12) = arctan(0.5) = 26.57°. For a 4:12 pitch: arctan(4/12) = 18.43°.
What is the pitch multiplier and why does it matter?
The pitch multiplier (also called slope factor) converts horizontal plan area to actual sloped roof area. Formula: Multiplier = √(1 + (Pitch ÷ 12)²). For a 6:12 roof it is 1.118, meaning a 1000 ft² footprint has 1118 ft² of roof surface. Ordering materials without the multiplier under-orders by 11.8% — enough to run short on a full roof.
At what pitch does a roof become non-walkable?
OSHA defines a steep roof as any roof steeper than 4:12 (18.4°), triggering fall protection requirements. Above 8:12 (33.7°), roof jacks and harnesses are standard practice. Above 10:12 (39.8°), the work becomes specialist — scaffolding or rope access is usually required.
How does roof pitch affect snow load?
Steeper roofs shed snow more effectively. Under ASCE 7, the snow load factor (Cs) reduces from 1.0 for slopes up to 30° to 0 for slopes above 70°. Most residential codes use a roof slope factor of 1.0 up to 30° (≈ 7:12), then reduce gradually. Check your local snow load map and code for the exact factor.
What is the best roof pitch for solar panels?
Optimal tilt equals your latitude — roughly 25°–40° in most of the US, Europe and Australia. A 6:12 pitch (26.57°) is close to optimal for most of the continental US and yields 95%+ of maximum production. Flatter or steeper roofs lose some output but are usually still viable for flush-mounted systems.
Why does the UK use different pitches to the US?
UK and Irish traditional roofs typically sit at 40°–50° because of higher rainfall, historic slate and clay tile materials, and building regulation BS 5534. US residential roofs cluster around 4:12 to 8:12 (18°–34°) because of different rainfall patterns, wider use of asphalt shingles, and lower material costs at shallower pitches.
More Online Calculators
References
- International Code Council. International Residential Code (IRC), Section R905 — Roof Assemblies. ICC, latest edition.
- International Code Council. International Building Code (IBC), Chapter 15 — Roof Assemblies and Rooftop Structures. ICC, latest edition.
- National Roofing Contractors Association. The NRCA Roofing Manual: Steep-Slope Roof Systems. NRCA, latest edition.
- ASCE/SEI 7-22. Minimum Design Loads and Associated Criteria for Buildings and Other Structures — Chapter 7: Snow Loads. American Society of Civil Engineers.
- Occupational Safety and Health Administration. 29 CFR 1926.500 — Fall Protection, and 29 CFR 1926.501 — Duty to Have Fall Protection. OSHA.
- British Standards Institution. BS 5534: Code of Practice for Slating and Tiling (including shingles). BSI.
- Standards Australia. AS 2050: Installation of Roof Tiles. Standards Australia.
- European Committee for Standardization. EN 1991-1-3: Eurocode 1 — Actions on Structures, Part 1-3: General Actions — Snow Loads. CEN.
- National Institute of Standards and Technology. NIST Special Publication 811 — Guide for the Use of the International System of Units (SI). NIST.
- ASTM International. ASTM E108 — Standard Test Methods for Fire Tests of Roof Coverings. ASTM.
Confirm pitch, material compatibility and snow load against the project specification and local building code before construction.