Roof Pitch Calculator
Calculate roof pitch from rise and run. Get pitch ratio, angle in degrees, slope percentage, rafter multiplier, roof classification, and walkability rating. Choose from 7 common presets or enter custom values.
📐 Roof Pitch Calculator
Pitch
Rafter
Classification
💡 Understanding Roof Pitch
Roof pitch is expressed as a ratio of vertical rise to horizontal run — for example, 6:12 means the roof rises 6 inches for every 12 inches of horizontal distance. In the US, pitch is always expressed over a 12-inch run. This ratio determines everything: material choices, walkability, cost, and structural requirements.
The pitch multiplier converts the flat (footprint) area into actual roof surface area. A 6:12 pitch has a multiplier of 1.118 — meaning the actual roof area is 11.8% larger than the footprint. This directly affects how many shingles, underlayment rolls, and other materials you need.
Estimate materials with our roofing calculator. Check snow loads with our roof snow load calculator. Size rafters with our lumber calculator.
Standard Roof Pitches
| Pitch | Angle (°) | Multiplier | Slope % | Classification | Walkable? |
|---|---|---|---|---|---|
| 0:12 | 0° | 1.000 | 0% | Flat | Yes — easy |
| 1:12 | 4.8° | 1.003 | 8.3% | Flat | Yes |
| 2:12 | 9.5° | 1.014 | 16.7% | Low slope | Yes |
| 3:12 | 14.0° | 1.031 | 25.0% | Low slope | Yes |
| 4:12 | 18.4° | 1.054 | 33.3% | Conventional | Yes — caution |
| 5:12 | 22.6° | 1.083 | 41.7% | Conventional | Yes — caution |
| 6:12 | 26.6° | 1.118 | 50.0% | Conventional | Moderate |
| 7:12 | 30.3° | 1.158 | 58.3% | Conventional | Moderate |
| 8:12 | 33.7° | 1.202 | 66.7% | Steep | Difficult |
| 9:12 | 36.9° | 1.250 | 75.0% | Steep | Roof jacks needed |
| 10:12 | 39.8° | 1.302 | 83.3% | Steep | Roof jacks needed |
| 12:12 | 45.0° | 1.414 | 100% | Very steep | Not walkable |
How to Measure Roof Pitch
Method 1: From the Roof
Hold a 12-inch level horizontally on the roof surface. At the 12-inch mark, measure straight down to the roof. That distance is the rise. If it measures 6 inches, your pitch is 6:12.
Method 2: From the Attic
Inside the attic, hold a level against a rafter. Measure 12 inches along the level from the rafter, then measure the distance from that point down to the rafter. This gives the rise without going on the roof — safer for steep roofs.
Method 3: Total Rise and Run
If you know the peak height and building width: Rise = peak height. Run = half the building width. Divide the rise (in inches) by the run (in inches) and multiply by 12 for the pitch. Example: 4 ft peak, 20 ft wide building → rise = 48", run = 120" → 48/120 × 12 = 4.8:12 pitch.
Method 4: Speed Square
Place the pivot point of a speed square on the rafter edge with a level attached. Read the degree marking where the rafter crosses the scale. Convert degrees to pitch using the table above or the formula: pitch = tan(degrees) × 12.
Converting Between Degrees and Pitch
Degrees → Pitch
Formula: Pitch = tan(angle°) × 12. Example: 30° → tan(30°) × 12 = 0.577 × 12 = 6.9:12.
Pitch → Degrees
Formula: Angle = arctan(rise ÷ 12). Example: 4:12 → arctan(4/12) = arctan(0.333) = 18.4°.
How Pitch Affects Cost
| Pitch Range | Cost Impact | Reason |
|---|---|---|
| 0–2:12 (Flat/Low) | Base cost | Easy to walk, no safety equipment |
| 3–5:12 (Low–Mid) | +5–10% | Slightly more material due to area increase |
| 6–8:12 (Conventional) | +10–20% | More materials, moderate safety needs |
| 9–12:12 (Steep) | +20–40% | Roof jacks, harnesses, slower work pace |
| 12:12+ (Very Steep) | +40–60% | Full scaffolding, specialized labor |
Roofing Material by Pitch
| Material | Minimum Pitch | Recommended Pitch |
|---|---|---|
| Built-up / TPO / EPDM (flat roofing) | 0.25:12 | 0.25–2:12 |
| Metal panels (standing seam) | 0.5:12 | 3:12+ |
| Asphalt shingles | 2:12 (with underlayment) | 4:12–12:12 |
| Wood shakes / shingles | 3:12 | 4:12–8:12 |
| Clay / concrete tile | 2.5:12 | 4:12–8:12 |
| Slate | 4:12 | 6:12–12:12 |
Common Roof Types by Pitch
- Flat roof (0–1:12): Commercial buildings, modern homes. Requires membrane roofing (TPO, EPDM). Must have positive drainage.
- Low slope (2–4:12): Ranch homes, attached garages. Can use shingles with proper underlayment. Minimum for most residential insurance.
- Conventional (5–8:12): Most common US residential range. Supports all roofing materials. Good balance of aesthetics, cost, and drainage.
- Steep (9–12:12): Cape Cod, Tudor, A-frame homes. Excellent snow shedding. Higher cost to install and maintain.
- Gambrel (dual-pitch): Barn-style. Lower section ~20:12, upper section ~7:12. Maximizes attic/loft space.
- Mansard (dual-pitch, 4 sides): Similar to gambrel but on all four sides. Very steep lower walls, flat or low-slope top.