Roofing Calculator

How to Use the Roofing Calculator

This calculator helps you determine how much roofing material you need for your project. Enter your roof dimensions, select the roof shape and pitch, choose your material type, and get an accurate estimate of bundles, sheets, or rolls required.

Step 1: Select Your Roof Shape

Choose the shape that best matches your roof:

• Gable Roof: The most common type with two sloping sides meeting at a ridge. Multiply the footprint by the pitch factor.
• Hip Roof: All four sides slope downward. Add 10% more material than a gable roof of the same size.
• Flat Roof: Minimal slope (typically less than 2/12). Material equals footprint area plus waste.
• Shed Roof: Single sloping surface, often used for additions. Calculate like one side of a gable roof.
• Gambrel Roof: Barn-style with two different slopes on each side. Requires 15% more material than a standard gable.

Step 2: Choose Your Roofing Material

Understanding Roof Pitch

Roof pitch is the slope expressed as rise over run. A 6/12 pitch means the roof rises 6 inches for every 12 inches of horizontal run. Steeper pitches require more roofing material because the actual surface area is larger than the horizontal footprint.

Common Roof Pitches and Multipliers

Waste Factor Guidelines

Always order extra material to account for cuts, overlaps, damaged pieces, and future repairs:

• 10% Waste: Simple rectangular roofs with minimal cuts
• 15% Waste (Recommended): Standard residential roofs with normal complexity
• 20% Waste: Complex roofs with valleys, dormers, or multiple hip sections
• 25% Waste: Very complex roofs with many angles and irregular shapes

Frequently Asked Questions

How many bundles of shingles do I need?

The number of shingle bundles depends on your roof area and pitch. Typically, 3 bundles cover 1 roofing square (100 sq ft). Calculate your total roof area, multiply by the pitch factor, add 15% for waste, then divide by the bundle coverage (usually 33.3 sq ft per bundle). Our calculator handles all this automatically.

What is a roofing square?

A roofing square is a unit of measurement equal to 100 square feet of roof area. Contractors and suppliers use squares to simplify ordering and pricing. For example, a 2,000 sq ft roof equals 20 squares. Most shingle bundles cover 1/3 of a square, so you need 3 bundles per square.

How do I measure my roof for materials?

Measure the length and width of your roof's horizontal footprint (ground-level dimensions). The calculator will adjust for roof pitch to get the actual surface area. For gable roofs, you can measure from the ground. For accuracy, measure from the roof if safely possible.

How much extra roofing material should I order?

For simple roofs, add 10% for waste. For standard residential roofs with typical complexity, 15% is recommended. For complex roofs with many valleys, dormers, or hip sections, add 20-25%. Extra material accounts for cuts, overlaps, damaged pieces, and future repairs.

What is roof pitch and how does it affect materials?

Roof pitch is the slope expressed as rise over run (e.g., 6/12 means 6 inches rise per 12 inches horizontal run). Steeper pitches require more material because the actual surface area is larger than the horizontal footprint. A 6/12 pitch increases material needs by about 12%, while a 12/12 pitch increases needs by 41%.

Should I include the eaves overhang when measuring a roof?

Include the overhang if you want the estimate to cover the full roof surface, not just the building footprint. Measure the roof’s horizontal length and width to the outer edge of the eaves, then account for pitch when estimating the sloped area. For a shed roof with a 12-foot run and a 1-foot overhang at each end, the measured run becomes 14 feet before applying the pitch factor.

How do I estimate roofing for a shed roof with a 6/12 pitch?

Measure the horizontal roof footprint, including overhang if you want it covered, then multiply the area by the pitch factor. A 6/12 pitch has a factor of about 1.118. For example, a 12-by-20-foot shed roof has a 240-square-foot footprint; its sloped area is about 268 square feet. Add the selected waste allowance before converting that area to bundles, sheets, or rolls.

Does a roof with two sides need twice the footprint area?

For a gable roof, the building footprint already represents the combined horizontal area of both roof slopes. Apply the pitch factor to that footprint to estimate the total sloped surface; do not double the footprint first. For example, a 20-by-30-foot footprint is 600 square feet, and a 6/12 pitch gives about 671 square feet before waste. Measure overhangs separately if they are part of the roof.