About the Roofing Calculator

A new roof is one of the largest home maintenance investments you'll make. Whether you're a homeowner getting estimates, a DIYer planning a project, or a contractor preparing a bid, knowing exactly how much material you need prevents costly overages and delays.

Our roofing calculator estimates:

Total roof area (accounting for pitch)
Shingles needed (in bundles or squares)
Underlayment (square footage)
Drip edge (linear feet)
Cost estimate based on material type

How to Calculate Roof Area

Step 1: Measure Building Footprint

Measure the length and width of your house at ground level.

Example: House is 40 ft long × 30 ft wide Footprint = 40 × 30 = 1,200 sq ft

Step 2: Account for Roof Pitch

Roof pitch is the rise over a 12-inch run. Steeper roofs have more surface area.

Pitch (Rise/12)	Multiplier	Angle
3/12 (low)	1.031	14°
4/12	1.054	18.4°
5/12	1.083	22.6°
6/12 (medium)	1.118	26.6°
7/12	1.158	30.3°
8/12	1.202	33.7°
9/12	1.250	36.9°
10/12	1.302	39.8°
12/12 (steep)	1.414	45°

Formula: Roof Area = Footprint × Pitch Multiplier

Example: 1,200 sq ft footprint, 6/12 pitch Roof Area = 1,200 × 1.118 = 1,342 sq ft

Step 3: Add Waste Factor

Complex roofs with valleys, hips, and dormers generate more waste.

Roof Complexity	Waste Factor
Simple gable roof	5-10%
Moderate complexity	10-15%
Complex (many valleys/dormers)	15-20%

Example: 1,342 sq ft with 10% waste Total = 1,342 × 1.10 = 1,476 sq ft

Roofing Materials Calculation

Asphalt Shingles

Shingles are sold by the "square" (100 sq ft of roof area).

Formula: Squares Needed = Total Roof Area ÷ 100

Example: 1,476 sq ft roof Squares = 1,476 ÷ 100 = 14.76 squares → round up to 15 squares

Bundles per square: Most shingles require 3 bundles per square. Total bundles: 15 × 3 = 45 bundles

Underlayment

Underlayment (felt or synthetic) covers the entire roof deck.

Example: 1,476 sq ft roof

Felt rolls (typically 432 sq ft per roll)
Rolls needed: 1,476 ÷ 432 = 3.4 → 4 rolls

Drip Edge

Drip edge runs along all roof edges.

Example: House 40 ft × 30 ft with 1-ft overhangs

Two long edges: 42 ft each = 84 ft
Two short edges: 32 ft each = 64 ft
Total drip edge: 148 linear feet
Standard drip edge comes in 10-ft lengths: 15 pieces

Roofing Material Costs

Material	Cost per Square	Lifespan	Best For
3-tab asphalt shingles	$80-120	15-20 years	Budget-conscious homeowners
Architectural shingles	$120-200	25-30 years	Most common choice
Premium shingles	$200-400	30-50 years	High-end homes
Metal roofing	$300-700	40-70 years	Durability, wildfire areas
Wood shakes	$350-600	20-40 years	Natural appearance
Clay/concrete tiles	$400-1,000	50-100 years	Spanish/mission style homes
Slate	$800-1,500+	75-200 years	Historic, premium homes

Total Cost Example

Project: 1,500 sq ft roof, architectural shingles

Item	Quantity	Unit Cost	Total
Shingles (15 sq)	15	$150/sq	$2,250
Underlayment	4 rolls	$50/roll	$200
Drip edge	150 ft	$1/ft	$150
Nails/flashing	-	-	$200
Ventilation	-	-	$150
Materials subtotal			$2,950
Labor (if hired)	15 sq	$300-500/sq	$4,500-7,500
Total project			$7,450-10,450

Roofing Tips

Get multiple quotes: Prices vary significantly between contractors.
Check ventilation: Proper attic ventilation extends roof life.
Remove old shingles: Installing over existing shingles is sometimes allowed but not recommended.
Check local codes: Some areas require specific materials or installation methods.
Time it right: Late spring through early fall is ideal for roofing in most climates.
Warranty matters: Look for 25-50 year material warranties and 5-10 year workmanship warranties.

DIY vs. Professional

Factor	DIY	Professional
Cost	Materials only ($3-5/sq ft)	$5-10/sq ft total
Time	Several weekends	1-3 days
Skill needed	Moderate	Already skilled
Safety risk	High (falls)	Managed with equipment
Warranty	Material only	Material + workmanship
Code compliance	Your responsibility	Contractor's responsibility

Recommendation: Unless you have roofing experience and proper safety equipment, hire a professional.

Frequently Asked Questions

What is a "square" in roofing?

A square = 100 square feet of roof area. It's the standard unit for ordering shingles.

How many bundles of shingles do I need?

Most asphalt shingles come 3 bundles per square. For a 20-square roof: 20 × 3 = 60 bundles.

How much does a new roof cost?

National average: $8,000-15,000 for asphalt shingles on a typical home. Metal, tile, and slate are significantly more.

How long does a roof last?

3-tab shingles: 15-20 years. Architectural shingles: 25-30 years. Metal: 40-70 years. Tile/slate: 50-100+ years.

Should I repair or replace my roof?

If your roof is near the end of its expected life, has widespread damage, or has been patched multiple times, replacement is usually more cost-effective than continued repairs.

Roofing Calculator