Roofing Calculator

Re-roofing your home or building a new one? Figuring out how many shingles to order starts with calculating the total roof area — adjusted for pitch. This roofing calculator handles all of that in seconds.

What Does This Calculator Do?

Enter your roof dimensions and pitch (slope), and the roofing calculator returns the total area in square feet and roofing squares (one roofing square = 100 sq ft). It also estimates the number of shingle bundles needed.

How to Use This Calculator

1. Measure the footprint of your roof from the ground (length × width of the building).
2. Enter the roof pitch (e.g., 6/12 means 6 inches of rise per 12 inches of run).
3. Click Calculate to get the actual sloped roof area.
4. Add 10–15% for waste (hips, valleys, and cuts).

Roofing Formula

Pitch Multiplier = √(1 + (Rise/Run)²)

Actual Roof Area = Footprint Area × Pitch Multiplier

Roofing Squares = Actual Roof Area ÷ 100

One bundle of standard 3-tab shingles covers about 33 sq ft, so 3 bundles = 1 square.

Example Calculation

Your home footprint is 40 ft × 30 ft = 1,200 sq ft. Roof pitch is 6/12.

• Pitch multiplier = √(1 + (6/12)²) = √1.25 ≈ 1.118
• Actual roof area = 1,200 × 1.118 = 1,342 sq ft
• Add 10% waste: 1,342 × 1.10 = 1,476 sq ft
• Roofing squares: 1,476 ÷ 100 = 14.76 squares
• Bundles needed: 14.76 × 3 = ~45 bundles

Why Use This Calculator?

Roofing materials are expensive, and a shortage mid-project means delays and potentially mismatched shingles. Accurate estimates upfront save money and headaches. Contractors use this same math for every bid.

Common Mistakes to Avoid

• Using floor area instead of roof footprint — include overhangs (eaves) in your measurement.
• Ignoring pitch — a steep roof has significantly more surface area than its footprint. A 12/12 pitch has 41% more area than a flat roof of the same footprint.
• Forgetting underlayment and flashing — calculate these separately; they're needed in addition to shingles.
• Not adding waste factor — complex roofs with hips and valleys need 15–20% extra.

Frequently Asked Questions

What is a roofing square?

A roofing square equals 100 square feet of roof surface. It's the standard unit roofing contractors use for pricing and ordering materials.

How many bundles of shingles per square?

Standard 3-tab shingles: 3 bundles per square. Architectural (dimensional) shingles: typically 3–4 bundles per square depending on the manufacturer.

What pitch is considered steep?

Roofs with a pitch of 7/12 or greater are considered steep. They require special safety equipment and may need additional labor costs.

Can I do this calculation for a hip roof?

Yes. Measure each roof plane separately, calculate each area (with pitch), and add them together. Hip roofs have four sloped planes instead of two.

How do I measure roof pitch?

Use a level and a ruler. Hold the level horizontally at the roof surface and measure 12 inches along the level. Then measure vertically from the end of the level down to the roof — that vertical measurement is your rise (e.g., 6 inches = 6/12 pitch).

Conclusion

Getting your roofing estimate right before you order materials keeps your project on schedule and on budget. Use this calculator whether you're DIY-ing a shed or working with a contractor on a full re-roof — the math is the same.

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