How do you calculate roof square footage?

Multiply the building footprint (length × width) by the pitch multiplier. The pitch multiplier accounts for the additional surface created by the slope: a 5/12 pitch multiplier is about 1.083, so a 40 × 30 ft building has 40 × 30 × 1.083 ≈ 1,300 sq ft of roof.

What is a "square" in roofing?

In roofing, one "square" equals 100 square feet of coverage. It is the unit roofers use to estimate materials and labor. A typical residential roof is 15–25 squares, or 1,500–2,500 sq ft.

How many shingles are in a bundle?

Most asphalt shingles come 3 bundles per square (100 sq ft). A bundle typically weighs 60–80 lbs and contains about 30 shingles. Architectural and luxury shingles can be 4 bundles per square.

How do I figure out my roof pitch?

Pitch is the vertical rise over a 12-inch horizontal run. Place a 12-inch level on the roof surface, then measure straight down from the level's far end to the roof. A 5-inch drop means a 5/12 pitch. You can also use a pitch gauge or smartphone level app for safety from the ground.

Why is the pitch multiplier important?

A roof's footprint (the area it shadows on the ground) is smaller than its actual surface area because the slope creates extra material. Steeper roofs need more shingles. Ignoring the multiplier under-orders material — a common mistake.

How much waste should I plan for roofing?

A simple gable roof needs about 10% waste for hip cuts, ridge caps, and starter strips. Hip roofs and complex roofs with valleys, dormers, or skylights need 15% or more because of the additional cuts at every plane intersection.

Does the calculator work for complex roofs with multiple sections?

This calculator handles simple gable and hip roofs. For complex roofs with dormers, multiple gables, or T- and L-shapes, calculate each section separately by treating each rectangular footprint as its own roof, then add the results together.

Outdoor Calculator

Roofing Square Footage Calculator

Get roof square footage, number of roofing squares, and shingle bundles needed for any simple gable or hip roof — with a built-in pitch multiplier.

Building Length (ft)

Building Width (ft)

Roof Pitch

Pitch is rise/run. A 5/12 pitch rises 5 inches every 12 inches of run.

Waste Allowance (%)

10% for simple gable roofs; 15% for hip roofs and complex layouts.

Note: This calculator assumes a simple gable or hip roof matching the building footprint. For complex roofs with dormers or valleys, calculate each plane separately and sum the areas.

Results

Building footprint1200 sq ft

Pitch multiplier× 1.083

Roof area (no waste)1300 sq ft

Roof + 10% waste1430 sq ft

Roofing squares14.30 sq

Shingle bundles (3/square)43 bundles

Underlayment rolls4 rolls

Roofing is sold in "squares": 1 square = 100 sq ft of coverage. Asphalt shingles come 3 bundles to a square. Synthetic underlayment typically covers ~400 sq ft per roll.

Roof Pitch Multipliers Reference

Pitch describes how steep the roof is, expressed as rise over a 12-inch horizontal run. The multiplier converts the building footprint area into actual roof surface area.

Pitch (rise/12)	Surface Multiplier	Equivalent Angle
1/12 (flat)	1.003	4.8°
3/12 (low)	1.031	14.0°
4/12 (standard)	1.054	18.4°
5/12 (standard)	1.083	22.6°
6/12 (standard)	1.118	26.6°
7/12 (steep)	1.158	30.3°
8/12 (steep)	1.202	33.7°
10/12 (very steep)	1.302	39.8°
12/12 (45°)	1.414	45.0°

Multiplier = √(1 + (rise/12)²). Use the multiplier closest to your measured pitch.

Roofing Material Yields

3-Tab Asphalt Shingles

3 bundles per square. Most economical option, 20–25 year warranty typical. Roughly $90–150 per square installed.

Architectural Shingles

3–4 bundles per square. Thicker dimensional appearance, 30-year warranty. About $130–200 per square installed.

Metal Roofing Panels

Sold by linear foot of panel; calculate roof area, then divide by panel width and order full lengths. 40–70 year service life.

Synthetic Underlayment

1 roll covers ~400 sq ft. Required beneath all shingle types. Replaces traditional 15 lb felt.

Frequently Asked Questions

Related Calculators

Planning the whole exterior? Pair this with deck, lawn, and concrete estimates.

Sources

The figures on this page are based on data from these authoritative industry sources.

The Home Depot Buyer’s Guides — Retail price ranges for flooring, paint, and finishing materials.

Roofing Square Footage Calculator

Results

Roof Pitch Multipliers Reference

Roofing Material Yields

3-Tab Asphalt Shingles

Architectural Shingles

Metal Roofing Panels

Synthetic Underlayment

Frequently Asked Questions

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Sources