Roofing Calculator
Calculate total roof pitch slope, total roof surface area, roofing squares, shingle bundle requirements, and underlayment felt rolls for residential and commercial roofing projects.
Calculate Roof Materials
Enter house footprint dimensions and roof pitch to estimate shingle requirements.
Calculation Results
Calculated using roof pitch geometric slope factor: Roof Area = (Length + Overhangs) × (Width + Overhangs) × Pitch Multiplier
Quick Summary
The Roofing Calculator estimates total roof surface area, roofing squares, 3-tab or architectural shingle bundle counts, and underlayment felt roll requirements by applying roof pitch geometric slope multipliers to building footprint dimensions.
- Roofing Square: The standard unit of roof measurement in North America (1 Square = 100 sq ft).
- Shingle Bundles: Most standard asphalt shingles require 3 bundles per roofing square (33.3 sq ft coverage per bundle).
- Pitch Slope Factor: Accounts for steepness (e.g. 6/12 pitch increases flat surface area by 1.118x).
How to Use the Roofing Calculator
- Enter the House Footprint Length in feet (e.g. 40 ft).
- Enter the House Footprint Width in feet (e.g. 30 ft).
- Enter the Roof Pitch / Slope rise number per 12" run (e.g. 6 for a 6:12 pitch).
- Enter the Overhang / Eaves width in feet (e.g. 1.5 ft).
- Click Calculate to view roofing squares, bundle counts, felt rolls, and cost estimates.
Roofing Formula & Method
Roof area calculation incorporates slope geometry using the Pythagorean theorem:
Total Footprint Area = (Length + 2 × Overhang) × (Width + 2 × Overhang)
Actual Roof Area (sq ft) = Total Footprint Area × Pitch Multiplier × 1.10 (Waste)
Roofing Squares = Actual Roof Area / 100
Shingle Bundles Needed = Roofing Squares × 3
Worked Example
Example: 40ft × 30ft House with 1.5ft Overhang and 6/12 Roof Pitch
- Total Footprint with Overhang: (40 + 3) × (30 + 3) = 43 ft × 33 ft = 1,419 sq ft
- Pitch Multiplier (6/12): ˆš(1 + (6/12)²) = ˆš(1.25) = 1.118
- Raw Roof Surface Area: 1,419 × 1.118 = 1,586.4 sq ft
- With 10% Waste Factor: 1,586.4 × 1.10 = 1,745 Sq Ft
- Roofing Squares: 1,745 / 100 = 17.45 Squares
- Shingle Bundles Needed: 17.45 × 3 = 53 Bundles
What This Calculator Includes vs. Does Not Include
What This Calculator Includes
- Pitch Slope Geometry Multiplier: Converts flat ground dimensions into true sloped roof surface area.
- Eave Overhang Inclusion: Adds exterior roof overhangs to building footprint.
- Shingle & Felt Roll Calculations: Computes bundles for asphalt shingles and rolls for #15 felt underlayment.
What This Calculator Does Not Include
- Dormers & Complex Valley Cuts: Intricate custom roof features require on-site contractor measurements.
- Rake & Starter Strip Nails: Roofing nails and flashing caps.
Tips & Best Practices
- Always Purchase Extra Starter Strips & Ridge Caps: Standard shingle bundles cover flat roof sections; hip and ridge cap shingles consume additional bundles.
- Use Synthetic Underlayment for High Slope Roofs: Synthetic underlayment provides superior water resistance and tear strength compared to traditional #15 felt.
Common Mistakes to Avoid
- Ignoring Roof Pitch: Measuring only flat ground footprint understates steep roof area by 20% to 40%.
- Forgetting Waste Factors on Hip Roofs: Hip and valley roofs produce significant cut waste, requiring a 15% waste margin compared to 10% for simple gable roofs.
Frequently Asked Questions (FAQ)
What is a square of roofing?
A roofing square is a unit of measurement equal to 100 square feet of roof surface area.
How many bundles of shingles are in a square?
There are 3 bundles of standard 3-tab or architectural asphalt shingles in 1 roofing square.
How many square feet does 1 bundle of shingles cover?
One bundle of shingles covers approximately 33.3 square feet of roof surface area.
How does roof pitch affect shingle requirements?
Steeper roof pitches increase the total surface area of a roof compared to its flat ground footprint, requiring more shingles.
What is a 6/12 roof pitch multiplier?
A 6/12 pitch has a multiplier of 1.118, meaning the roof surface is 11.8% larger than its flat horizontal footprint.
How many rolls of underlayment felt do I need?
A standard roll of #15 felt covers 400 sq ft, while #30 felt covers 200 sq ft. Divide total roof area by roll coverage.
What waste factor should I use for a hip roof?
Use a 15% waste factor for hip and valley roofs due to diagonal cuts, compared to 10% for simple gable roofs.
How much does a square of asphalt shingles cost?
Asphalt shingles cost between and per square for materials alone, or to per square installed with labor.
Is this roofing calculator free to use?
Yes, TibCal's Roofing Calculator is 100% free with no sign-up required.