Roofing Calculator
Calculate roofing material needed in squares (100 sq ft) for any roof pitch.
The Formula
Squares = Roof Area / 100
Pitch factor: 4/12 = 1.054 · 6/12 = 1.118 · 8/12 = 1.202
1 roofing square = 100 ft²
Roof area = 1,500 × 1.118 = 1,677 ft²
Squares = 1,677 / 100 = 16.77
+ 10% waste = 18.5 squares
Understanding Roofing Squares
Roofing materials — shingles, underlayment, and flashing — are measured and sold in squares, where one square covers exactly 100 square feet. To estimate your roof accurately, you need two things: the footprint area of the home (the area of the house as seen from above) and the pitch of the roof. A steeply pitched roof has significantly more actual surface area than the footprint suggests, so a pitch multiplier is applied to convert footprint area to actual roof area.
Roof Pitch and Pitch Multipliers
Roof pitch is expressed as rise over run — a 6:12 pitch rises 6 inches for every 12 horizontal inches. The pitch multiplier adjusts for the extra surface area created by the slope: a flat roof (1:12) has a multiplier of 1.00. A 4:12 pitch (common on ranch homes) is about 1.054. A 6:12 pitch (moderate) is about 1.118. A 12:12 pitch (steep, 45 degrees) is about 1.414. Multiply your footprint area by the multiplier to get actual roof area, then divide by 100 for squares.
What to Order Beyond Shingles
A complete roofing project needs more than shingles. Underlayment (synthetic or felt) goes under the shingles and provides a moisture barrier — plan for one full layer across the entire roof. Ridge cap shingles cover the peak and hips of the roof and are sold separately from field shingles. Drip edge goes along the eaves and rakes to direct water away from the fascia. Flashing is needed around chimneys, vents, and valleys. Always add 10–15% to your material estimate for waste, overlaps, and starter strips.
Frequently Asked Questions
How many shingles are in a roofing square?
Three bundles of standard three-tab asphalt shingles cover one square (100 square feet). Architectural (dimensional) shingles may require 4 bundles per square — always check the manufacturer's specifications, as coverage varies by product. When in doubt, buy more than you think you need; leftover bundles can be returned or stored for repairs.
What is a good roof pitch for a house?
Most residential roofs use a 4:12 to 8:12 pitch. The 4:12 to 6:12 range is the most common for standard asphalt shingles and balances material cost, weather performance, and ease of installation. Steeper pitches shed water and snow more effectively and can look more dramatic architecturally, but they increase material cost and make installation more dangerous. Very low slopes (under 2:12) require special low-slope roofing materials.
How long does a roof last?
Standard three-tab asphalt shingles last 15–25 years. Architectural/dimensional shingles last 25–30 years. Premium impact-resistant shingles can last 30–50 years. Metal roofing lasts 40–70 years. Slate and clay tile can last over 100 years with proper maintenance. Climate, ventilation, and installation quality all significantly affect actual lifespan.
Can I roof over old shingles?
Most building codes allow one layer of new shingles over an existing layer. Adding a second overlay over two existing layers is not permitted in most jurisdictions. Roofing over old shingles saves the cost of tear-off and disposal but can trap moisture, reduce the new roof's lifespan, void warranties, and hide underlying deck problems. Full tear-off is generally recommended for the best long-term outcome.
How much does a new roof cost?
Roofing costs vary widely by region, materials, and roof complexity. A typical 2,000 square foot home might have 20–25 squares of roof area. With architectural shingles, full installation typically runs $8,000–$15,000 for an average home. Metal roofing runs $15,000–$30,000+. Always get at least three written estimates from licensed roofers and verify they carry workers' compensation and liability insurance.