Roof Square Footage Calculator (Canada)

Free roof square footage calculator for Canadian projects. Get on-slope area in sq ft, asphalt shingle bundles, and ice & water shield rolls. NBC 9.26 compliant with snow load notes.

Roof Square Footage Calculator

Footprint length (ft) Footprint width (ft) Pitch (X/12) Overhang (ft)

Roof surface area

1503

square feet

Roofing squares

15.03

1 square = 100 sq ft

Bundles needed

3 bundles per square + 10% waste

How to use this calculator

Measure your home’s exterior footprint at the gutter line:

Footprint length — the longest exterior dimension in feet
Footprint width — the shorter exterior dimension in feet
Pitch (X/12) — Canadian convention follows the US X/12 system; degrees also accepted
Overhang — typical 1 to 2 ft on residential roofs (deeper in heavy-snow regions)

The calculator returns:

Roof surface area in square feet (the actual area you cover)
Roofing squares (sq ft / 100, the unit Canadian roofers price)
Bundle count (with 10 percent waste already included)
Ice & water shield linear feet at the eaves

Why this calculation gets done wrong on Canadian quotes

Two common errors:

Error 1: Quoting from footprint instead of on-slope area. A 1,500 sq ft Calgary bungalow at 8/12 pitch has 1,800 sq ft of actual roof. Quoting from footprint underorders by 20 percent — that is 6 missing squares, or roughly $1,800 in IKO Dynasty material at current Home Depot Canada pricing.

Error 2: Underestimating ice and water shield. NBC requires 600 mm inside the wall, but in Ottawa, Quebec City or anywhere east of Sault Ste Marie, smart roofers run ice and water shield 1.2 m up from the eave plus into all valleys. Skimping here causes interior leaks during the spring thaw — and the warranty repair eats any savings ten times over.

The formula

Footprint (sq ft) = (length + 2×overhang) × (width + 2×overhang)
Slope factor = √(1 + (pitch/12)²)
Roof surface area = footprint × slope factor
Squares = surface area / 100

The calculator does the maths; you supply the four inputs.

How material counts work in Canada

Asphalt architectural shingles (IKO Cambridge, BP Mystique 42, GAF Timberline HDZ, CertainTeed Landmark): 3 bundles per square, plus 10 percent waste. Each bundle weighs about 70 to 80 lb, so a 25-square roof needs 75 bundles — about 5,800 lb total weight on the roof deck.

Premium laminate shingles (IKO Dynasty, BP Mystique 50, CertainTeed Landmark Pro): 4 bundles per square. Heavier and higher wind rating, important in Atlantic Canada and Prairies.

Underlayment (synthetic, Tyvek Protec or Owens Corning ProArmor): 1 roll covers 10 squares (1,000 sq ft per roll for synthetic).

Ice and water shield (Grace Ice & Water Shield, IKO StormShield): 1 roll = 200 linear feet at 36 inches wide. NBC requires from eave to 600 mm inside the wall, so on a 40-ft eave you need about 12 ft up the slope of coverage = 480 sq ft = roughly 2.5 rolls.

Drip edge: linear feet around perimeter. For a 40x30 home with 1.5 ft overhang, perimeter = 2 × (43 + 33) = 152 linear feet, ordered as 10-ft pieces.

Ridge cap: linear feet of ridges. Use Hip & Ridge shingles (matching, premium) at 4 lf per shingle.

Starter strip: linear feet of eaves — usually building length × 2.

Adjusting for complex Canadian roofs

Hip roof (very common in newer subdivisions across Canada): same calc — on-slope area equals the gable equivalent.
L-shape or T-shape: split into rectangles, calculate each, sum.
Steep Quebec mansard: use the gambrel roof calculator for the upper/lower pitch combo.
Heritage Victorian with dormers: add 15 to 20 percent waste instead of 10 percent for valley and dormer cuts.

Snow load and pitch — Canadian considerations

NBC 9.26 and provincial supplements set snow loads by region. In Quebec City, ground snow load is 4.5 kPa; in Vancouver only 1.6 kPa. Steeper pitches shed snow faster and reduce dead load on rafters — but they also need premium shingles rated for ice damming and wind uplift. The calculator does not compute structural load; consult an engineer if your design exceeds the NBC Part 9 prescriptive tables.

Sources used in this calculator

Slope factor maths is universal trigonometry. Bundle-per-square coverage rates come from IKO Canada, BP Canada, CertainTeed Canada and GAF technical data sheets. Ice and water shield requirements reference NBC 9.26.5 and Ontario Building Code 9.26.5.5. Pricing benchmarks come from CRCA member surveys and HomeStars contractor quotes across major Canadian markets.

For per-square installed pricing in your area, Renomii and HomeStars publish provincial averages; get at least three written quotes from CRCA member contractors.

Frequently asked questions

How do I calculate roof square footage for a Canadian home?

Multiply the building footprint length by width, then multiply by the slope factor for your pitch. A 40x30 ft Toronto bungalow at 6/12 pitch has a 1,200 sq ft footprint and a 1.118 slope factor, giving about 1,341 sq ft of roof area before adding the eave overhang.

What is a roofing square in Canada?

Same as in the US: 1 roofing square equals 100 square feet of roof surface. Canadian shingle suppliers (BP Canada, IKO, GAF, CertainTeed) all quote in squares and bundles. A typical 1,800 sq ft bungalow in the GTA has a 22 to 28 square roof depending on pitch and eaves.

How many bundles of shingles per square in Canada?

IKO Cambridge architectural and BP Mystique 42 both run 3 bundles per square (76.5 sq ft per bundle for Cambridge). Heavier laminates like IKO Dynasty are 4 bundles per square. Always order 10 percent extra for waste, plus another 5 percent for hip and valley cuts. The calculator adds 10 percent by default.

Do Canadian building codes require ice and water shield?

Yes. NBC 9.26.5 and most provincial codes (Ontario OBC 9.26.5, Quebec CCQ) require ice and water shield from the eave to at least 600 mm inside the exterior wall line. In snow belt regions (Sault Ste Marie, Sudbury, Quebec north shore) double-coverage to 900 mm or more is common. The calculator outputs the linear footage of eaves so you can order rolls.

Should I include the eave overhang?

Yes. Canadian eaves typically project 12 to 24 inches (305 to 610 mm) for snow shedding and ice damming protection. On a 40x30 footprint a 16-inch overhang adds about 168 sq ft (14 percent). Critical in Manitoba, Saskatchewan and Quebec where eave protection is non-negotiable.

Roof Square Footage Calculator (Canada)