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Roofing Calculator

Roofing materials are sold by the 'square' — a unit equal to 100 square feet. This calculator takes your roof dimensions and pitch to estimate materials including shingle bundles, underlayment, and ridge cap.

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Results

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How to Use This Calculator

  1. Measure the length of your roof (ridge line) in feet.
  2. Measure the width from eave to ridge on one side.
  3. Enter the roof pitch (rise per 12 inches of run).
  4. Adjust the waste percentage if needed (10% is standard).
  5. Review squares and bundle estimates.

How Roofing Calculation Works

Roof pitch affects actual surface area — a steeper roof has more area than the flat footprint suggests. This calculator uses a pitch multiplier derived from the Pythagorean theorem to convert flat area to actual roof area. It assumes a simple gable (two-sided) roof. Complex roofs with hips, valleys, and dormers require additional material — increase the waste factor to 15–20% for these. Three bundles of standard 3-tab shingles equal one square (100 sq ft).

Formula

Flat area = Length × Width. Pitch multiplier = √(1 + (pitch/12)²). Actual area = Flat area × Pitch multiplier × 2 (for both sides of a gable roof). Squares = Actual area ÷ 100. Bundles = Squares × 3. Add waste factor.

Frequently Asked Questions

What is a roofing square?
A roofing square is a unit of measurement equal to 100 square feet of roof area. Roofing materials including shingles, underlayment, and flashing are all priced and sold by the square.
How many bundles of shingles per square?
Standard 3-tab shingles come 3 bundles per square (100 sq ft). Architectural/dimensional shingles vary — some are 3 bundles per square, heavier ones may be 4–5 bundles per square. Check the manufacturer's specs.
How do I measure roof pitch?
From inside the attic, place a level horizontally against a rafter. Measure 12 inches along the level, then measure the vertical distance from that 12-inch mark up to the rafter. That vertical distance is the pitch (e.g., 6 inches = 6/12 pitch).
How much does a new roof cost?
Asphalt shingle roofs typically cost $5,000–$12,000 for a standard home (1,500–2,500 sq ft roof area), or roughly $3–$5 per square foot installed. Metal roofing runs $8–$14 per square foot. Prices vary significantly by region and roof complexity.

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