Roofing Calculator

How many roofing squares do I need? Multiply building footprint length × width by the pitch factor sqrt(1 + (rise/12)²), add waste (default 10%), then divide by 100 for squares and multiply by 3 for bundles. A 40×24 ft roof at 6/12 with 10% waste is about 1,181 sq ft — 12 squares, 36 bundles.

Reviewed / updated August 2026

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Your inputs

ft

Building length in feet (plan view)

ft

Building width in feet (plan view)

Rise over 12″ of run — e.g. 6/12 is a common residential pitch

%

Default 10% for cuts, starter, and simple hips/valleys

Result

Roofing to order

12 squares

36 bundles · 1181 sq ft with waste

Roof area (surface)
1073 sq ft
With waste
1181 sq ft
Squares (100 sq ft)
12
Bundles (×3)
36
6/12 pitch factor
1.118

A 6/12 roof on this footprint has about 1073 sq ft of surface. With waste, plan on 1181 sq ft — 12 squares (36 bundles at 3 per square).

What-if: 4/12 vs 8/12 on this footprint

PitchAreaSquaresBundles
4/121113 sq ft1236
8/121269 sq ft1339

Suggested next step

Steeper roofs need more surface and safer staging — confirm bundle counts before delivery day.

How the roofing calculation works

Roofing material is sold by the square (100 sq ft) and by the bundle. Because a pitched roof is longer than its floor plan, we scale the footprint by a pitch factor:

  1. Pitch factor = √(1 + (rise ÷ 12)²) — the secant of the roof angle
  2. Roof area = length × width × pitch factor
  3. With waste = roof area × (1 + waste% ÷ 100)
  4. Squares = ceil(with waste ÷ 100)
  5. Bundles = squares × 3 (common asphalt packaging)

Results update as you change footprint, pitch (2/12–12/12), or waste. Compare 4/12 vs 8/12 on the same plan to see how steepness changes bundle counts. Pair with the Lumber Calculator for fascia and the Home Improvement hub for related DIY tools.

Source note: Pitch geometry is standard right-triangle roof math; bundle-per-square assumes typical 3-bundle asphalt packaging. Updated August 2026.

Worked example

Building footprint 40 × 24 ft, pitch 6/12, waste 10%:

  1. Pitch factor = √(1 + 0.25) ≈ 1.118
  2. Roof area ≈ 960 × 1.118 ≈ 1,073 sq ft
  3. With waste ≈ 1,073 × 1.10 ≈ 1,181 sq ft
  4. Squares = ceil(1,181 ÷ 100) = 12
  5. Bundles = 12 × 3 = 36

Those are the default inputs on this page. Steeper pitches increase surface area without changing the footprint — use the what-if table before you order.

Methodology and notes

This model treats the roof as a single pitched plane over a rectangle. Multi-section roofs, dormers, and heavy valley work need extra waste. Always confirm product coverage on the wrapper and follow manufacturer pitch limits for warranties.

Frequently asked questions

How do you calculate roofing squares?

Find roof surface area (footprint × pitch factor), multiply by (1 + waste%), then divide by 100 and round up. One square = 100 square feet of roof coverage.

How many bundles of shingles per square?

Most asphalt architectural shingles are packaged so three bundles cover about one square. Always check the bundle label — some products differ.

What is a 6/12 roof pitch?

The roof rises 6 inches for every 12 inches of horizontal run. The pitch factor is sqrt(1 + (6/12)²) ≈ 1.118, so surface area is about 11.8% larger than the flat footprint.

Why add 10% waste?

Waste covers starter course, ridge, hips, valleys, and cut-offs. Complex roofs may need 15% or more; simple gables sometimes get by with less.

Does this include underlayment?

No. This estimate is for field shingle coverage (squares/bundles). Order underlayment, ice & water shield, drip edge, and ridge cap separately.

Related tools

Related calculators — live tools and upcoming pages for internal linking.