Roof Pitch Calculator
Convert between rise over 12, degrees, percentage grade and the slope factor — then get rafter lengths and real roof area.
The Roof Pitch Calculator runs entirely in your browser. Your measurements never leave your device.
Open the Roofing Calculator
Roof Pitch Calculator について
Roof pitch is one angle with four names. Roofers write it as rise over a 12-inch run, drawings mark it in degrees, surveys use a percentage grade, and estimators need the slope factor — the multiplier that turns a floor plan's square footage into the roof surface you actually buy material for. This calculator converts all four in both directions, then applies them: rafter length for a symmetrical gable, the longer hip or valley rafter that runs diagonally across two slopes at once, and the sloped area and roofing squares for a given footprint. It also flags where a pitch falls below what shingles are rated for, which is the point at which the material choice changes.
機能
- Rise per 12, degrees, percentage grade and slope factor, converted both ways
- Hip and valley factor, which is always larger than the common slope factor
- Common rafter length with and without the eave overhang
- Ridge height above the wall plate for any span
- Footprint area converted to sloped roof area and roofing squares
- Material advice at the 2/12 and 4/12 thresholds
- One-tap presets for the pitches actually built
- Everything converts in your browser
Roof Pitch Calculator の使い方
- Choose whether you know the pitch, the angle or the grade
- Enter the value, or tap a common pitch
- Add the building span and overhang for rafter lengths
- Enter the footprint area to get the real roof area
例
入力
6/12 pitch · 24 ft span · 1 ft overhang · 1,200 sq ft footprint
出力
26.57° · 50% grade · slope factor 1.1180 · hip factor 1.5
Rafter 13.42 ft (14.53 with overhang) · roof area 1,342 sq ft = 13.42 squares
The slope factor multiplies plan area, never the eave length.
よくあるエラーとトラブルシューティング
- The roof area came out larger than the building footprint. — It should. A sloped surface is longer than its horizontal projection, so a 6/12 roof covers 11.8% more area than the plan it sits on. That difference is exactly what the slope factor is for.
- The hip rafter measured longer than calculated. — Check you used the hip and valley factor rather than the common slope factor. A hip runs diagonally across two slopes, so it uses a run of √2 × 12 rather than 12, and comes out noticeably longer.
- Shingles were quoted for a very low-slope roof. — Asphalt shingles are not permitted below 2/12 and need a doubled underlayment between 2/12 and 4/12. Below that, a membrane, modified bitumen or standing-seam metal is the correct product.
よくある質問
- What is a 6/12 roof pitch in degrees?
- 26.57°. The pitch is the tangent of the angle, so 6 divided by 12 gives 0.5, and the arctangent of 0.5 is 26.57 degrees. That also makes it a 50% grade.
- What is the slope factor and how do I use it?
- It is the ratio of sloped length to horizontal run — √(rise² + 12²) ÷ 12. Multiply the footprint area by it to get the actual roof surface, which is what shingle and underlayment quantities are based on.
- What roof pitch is 45 degrees?
- 12/12, where the rise equals the run. Its slope factor is √2, about 1.414, so a 45° roof has 41% more surface than the ground it covers.
- What is the minimum pitch for asphalt shingles?
- 2/12 is the absolute minimum permitted, and only with two layers of underlayment. 4/12 and above is standard practice, where a single underlayment and normal shingle installation are approved.
- How do I measure roof pitch without climbing on the roof?
- Hold a level against a rafter or gable end, mark 12 inches along it, and measure straight down from that mark to the roof surface. That vertical measurement in inches is the rise per 12 of run.
関連ツール
- 屋根面積計算ツール — 設置面積と勾配から屋根面積・スクエア・束数を見積もる。
- 階段計算機 — 段数・蹴上げ・踏面・側桁の長さを計算します。
- 平方フィート計算機 — フィートまたはメートルで面積を計算、コストも見積もり。
- Deck Calculator — Boards, joists, footings and screws for a deck, with joist spans checked.
- R値計算 — 層を積み上げてU値と熱損失を計算します。
- アスファルト計算 — 厚みに応じたアスファルトのトン数と費用を計算します。
すべての ArrayKit ツール