# Roofing and shingle calculator

> Roof area, squares and shingle bundles from building size and pitch, with underlayment rolls, ridge cap and the IRC minimum slope check.

ஊடாடும் பதிப்பு: https://www.calcopenly.com/ta/construction/roofing-calculator
பாடப்பிரிவு: கட்டுமானம் மற்றும் வீட்டுக் கணிப்பான்கள்

Roof area is the footprint including overhangs multiplied by the slope factor √(1 + (rise ÷ 12)²), which turns plan area into sloped surface. A hip roof with the same pitch on all four sides has the same factor as a gable. Area plus waste is divided into squares of 100 ft² and multiplied by bundles per square; the ridge and hip length divided by the coverage of one ridge-cap bundle gives the ridge bundles.

The default 40 × 30 ft gable with 1 ft overhangs at a 6/12 pitch has a slope factor of 1.118 and 1,502.64 ft² of roof. With 10% waste that is 16.53 squares, or 50 bundles at three per square, plus 4 rolls of #15 felt and 2 bundles of ridge cap.

The pitch is checked against the asphalt-shingle slope rules in 2021 IRC R905.2.2. Valleys, dormers, starter strip and drip edge are not counted.

## உள்ளீடுகள்

- **Roof type** (விருப்பங்கள்: Gable, Hip)
- **Building length**
- **Building width**
- **Overhang on each side**
- **Pitch given as** (விருப்பங்கள்: Rise per 12, பாகைகள்)
- **Pitch**
- **Pitch angle**
- **Waste allowance**
- **Bundles per square**: Three bundles cover one square (100 ft²) for most 3-tab and architectural shingles.
- **Underlayment** (விருப்பங்கள்: #15 felt (4 squares per roll), #30 felt (2 squares per roll), Synthetic (10 squares per roll))
- **Ridge cap per bundle**: Read it on the wrapper: GAF Seal-A-Ridge covers about 25 ft, Owens Corning ProEdge about 33 ft.

## முடிவுகள்

- Shingle bundles to buy (bundles) — முதன்மை முடிவு
- Roof area (ft²)
- Roof area (m²)
- Squares with waste (squares)
- Underlayment rolls (rolls)
- Ridge and hip length (ft)
- Ridge and hip length (m)
- Ridge cap bundles (bundles)
- Pitch angle (°)
- Pitch (in 12)
- Slope factor

## சூத்திரம்

$$
A = (L + 2o)(W + 2o)\sqrt{1 + (p/12)^2},\qquad \text{bundles} = \left\lceil 3 \cdot \frac{A (1 + \text{waste})}{100} \right\rceil
$$

## தீர்க்கப்பட்ட எடுத்துக்காட்டுகள்

### 40 × 30 ft gable, 1 ft overhang, 6/12, 10% waste

- Roof type: Gable
- Building length: 40 ft
- Building width: 30 ft
- Overhang on each side: 1 ft
- Pitch given as: Rise per 12
- Pitch: 6 in 12
- Waste allowance: 10%
- Underlayment: #15 felt (4 squares per roll)
- **Roof area: 1,502.6 ft²**
- **Squares with waste: 16.53 squares**
- **Shingle bundles to buy: 50 bundles**
- **Underlayment rolls: 4 rolls**
- **Ridge and hip length: 42.0 ft**
- **Ridge cap bundles: 2 bundles**
- **Pitch angle: 26.6 °**
- சரிபார்ப்பின் மூலம்: Python decimal: 42 × 32 × √1.25 = 1502.64 ft²; × 1.1 ÷ 100 × 3 = 49.59 → 50 bundles; 15.03 squares ÷ 4 → 4 rolls

### Hip roof 40 × 30 ft, 6/12, no overhang or waste

- Roof type: Hip
- Building length: 40 ft
- Building width: 30 ft
- Overhang on each side: 0 ft
- Pitch given as: Rise per 12
- Pitch: 6 in 12
- Waste allowance: 0%
- Underlayment: #15 felt (4 squares per roll)
- **Roof area: 1,341.6 ft²**
- **Ridge and hip length: 100.0 ft**
- **Shingle bundles to buy: 41 bundles**
- சரிபார்ப்பின் மூலம்: Hand calculation: ridge 40 − 30 = 10 ft; each hip √(2 × 15² + 7.5²) = 22.5 ft, × 4 = 90 ft; 1200 × 1.118034 = 1341.64 ft²

### Edge: 12/12 pitch is 45°

- Roof type: Gable
- Building length: 30 ft
- Building width: 20 ft
- Overhang on each side: 0 ft
- Pitch given as: Rise per 12
- Pitch: 12 in 12
- Waste allowance: 0%
- Underlayment: #15 felt (4 squares per roll)
- **Roof area: 848.5 ft²**
- **Pitch angle: 45.0 °**
- **Slope factor: 1.4142**
- **Shingle bundles to buy: 26 bundles**
- சரிபார்ப்பின் மூலம்: Hand calculation: slope factor √2 = 1.41421; 600 × √2 = 848.53 ft² → 25.46 → 26 bundles

### 30° roof on a 10 × 8 m house, 0.5 m overhang

- Roof type: Gable
- Building length: 10 m
- Building width: 8 m
- Overhang on each side: 0.5 m
- Pitch given as: பாகைகள்
- Pitch angle: 30 °
- Waste allowance: 10%
- Underlayment: #15 felt (4 squares per roll)
- **Roof area: 114.32 m²**
- **Shingle bundles to buy: 41 bundles**
- சரிபார்ப்பின் மூலம்: Python math: 11 × 9 m ÷ cos 30° = 114.3154 m² = 1230.48 ft² × 1.1 ÷ 100 × 3 = 40.6 → 41

## கேள்விகள்

### How many bundles of shingles do I need?

Divide the roof area by 100 to get squares, add waste, and multiply by the bundles per square printed on the wrapper (three is the default here). A 40 × 30 ft gable with 1 ft overhangs at 6/12 has 1,502.64 ft² of roof, or 16.53 squares with 10% waste: 49.6 bundles, bought as 50. The waste presets are 10% for gables and 15% for hips, where every course is cut along the hips.

### How do you convert roof pitch to degrees and a slope factor?

Pitch is the rise in inches per 12 in of run. A 6/12 roof rises at arctan(6 ÷ 12) = 26.57°, and its slope factor √(1 + 0.5²) = 1.118 means each square foot of plan carries 1.118 ft² of roof. A 4/12 roof is 18.43° with a factor of 1.054; a 12/12 roof is 45° with a factor of 1.414.

### What is the minimum roof pitch for asphalt shingles?

2:12, about 9.5°. Under 2021 IRC R905.2.2, asphalt shingles may be used only on slopes of 2 in 12 or steeper, and slopes from 2:12 up to 4:12 need double underlayment. Flatter roofs need a low-slope covering such as a membrane. In the 2:12 to 4:12 range this calculator doubles the underlayment rolls.

### What is a roofing square?

100 ft² of roof surface, about 9.29 m². Shingles and underlayment are ordered by the square, so a roof of 1,502.64 ft² is 15.03 squares before waste and 16.53 after 10% waste. With the #15 felt option at 4 squares per roll, that roof takes 4 rolls of underlayment.

### How do you calculate the area of a hip roof?

Use the same slope factor as a gable: when all four sides share one pitch, sloped area = plan area × √(1 + (rise ÷ 12)²). A 40 × 30 ft hip roof at 6/12 with no overhang is 1,200 × 1.118 = 1,341.64 ft². Its ridge is 40 − 30 = 10 ft and each of the four hips is 22.5 ft, so ridge cap covers 100 ft.

### “Roofing and shingle calculator” எவ்வளவு துல்லியமானது?

துல்லியம் உங்கள் உள்ளீடுகளையும் முறையின் அனுமானங்களையும் சார்ந்தது. தசமக் கணக்கீடு 50 முக்கிய இலக்கங்களைப் பயன்படுத்துகிறது. ஆனால் மதிப்பீடுகள், எண் முறைகள், மூலத் தரவுகள் குறைந்த துல்லியத்தைக் கொண்டிருக்கலாம்; காட்டப்படும் மதிப்பை வட்டமிடுவது இந்த வரம்புகளை நீக்காது. சுயாதீன மூலங்களின் தீர்வுகளுடன் சரிபார்க்கப்பட்ட எடுத்துக்காட்டுகள்: 4. எடுத்துக்காட்டாக, “40 × 30 ft gable, 1 ft overhang, 6/12, 10% waste” என்பது Python decimal: 42 × 32 × √1.25 = 1502.64 ft²; × 1.1 ÷ 100 × 3 = 49.59 → 50 bundles; 15.03 squares ÷ 4 → 4 rolls உடன் சரிபார்க்கப்படுகிறது.

### இந்த முறையின் மூலம் என்ன?

International Code Council — 2021 IRC R905.2.2: asphalt shingles on slopes of 2:12 or steeper, double underlayment from 2:12 up to 4:12; GAF Seal-A-Ridge — 25 linear ft per bundle; Owens Corning ProEdge — 33 linear ft per bundle.

## ஆதாரங்கள்

- International Code Council — 2021 IRC R905.2.2: asphalt shingles on slopes of 2:12 or steeper, double underlayment from 2:12 up to 4:12
- [GAF Seal-A-Ridge — 25 linear ft per bundle; Owens Corning ProEdge — 33 linear ft per bundle](https://www.owenscorning.com/en-us/roofing/components/products/proedge-hip-ridge)