Roofing Calculator

1. Calculating Roof Area

A roof is rarely flat. The steepness (pitch) increases the surface area compared to the flat footprint of the house.

Formula: Roof Area = Base Area × Pitch Multiplier

2. Understanding Pitch

Pitch is measured by how many inches the roof rises for every 12 inches of horizontal run.

• 4:12 is a common, walkable pitch.
• 6:12 to 9:12 is moderate but harder to walk on.
• 10:12+ is steep and requires safety gear.

3. What is a "Square"?

In roofing terms, a Square equals 100 square feet of roof area. Suppliers sell materials based on squares.

• Shingles: Typically 3 bundles cover 1 square.
• Felt/Underlayment: One roll often covers 2-4 squares depending on overlap.

4. Waste Factor

Always buy extra material to account for cutting, mistakes, and hips/valleys.

• 5-10%: Simple gable roofs.
• 10-15%: Hip roofs or roofs with dormers.
• 15-20%: Complex roofs with many valleys.