NRCA Roofing Manual • IRC R905Pitch Multiplier: 1.054

How Many Squares & Bundles of Shingles for a 1800 Sq Ft Roof?

For a 1800 sq ft house footprint with a 4:12 roof pitch and standard 12" eave overhangs, the true slope surface area is 2049 sq ft. Incorporating a 10% waste buffer for cut-offs and valleys, your order requires exactly:

Custom Roofing Engine

Roofing Squares

100 sq ft each

Shingle Bundles

3 bundles / sq

Synthetic Felt

Rolls (400 sq ft)

Est. Materials

$3,105

Full BOM package

Complete Roofing Material Takeoff & Bill of Materials

Order checklist covering primary shingles, underlayment, and edge flashing

Item / Description	Quantity	Est. Unit Price	Total Est. Cost	Application Notes
Architectural Laminated Asphalt ShinglesLifetime Limited Warranty, 3 bundles per square, class A fire rating	69 Bundles	$36	$2,484	Covers 23 squares (2254 sq ft) with 10% waste factor
High-Tear Synthetic Roofing UnderlaymentClass A fire rating, UV resistant 180 days, 10-mil thickness (400 sq ft/roll)	6 Rolls	$78	$468	Full deck protection for 2049 sq ft of roof sheathing
Self-Adhering Ice & Water Shield MembraneRubberized asphalt membrane, 36" × 66 ft (200 sq ft roll), IRC R905 compliant	2 Rolls	$110	$220	Applied along eaves (24" inside heated wall line) and valleys
Universal Starter Shingle StripsAggressive factory sealant strip, 105 linear ft per bundle	2 Bundles	$48	$96	Locks down bottom perimeter along 117 ft of eaves
Specialty Hip & Ridge Cap ShinglesPre-cut shadow-accent ridge shingles, 33 linear ft coverage per bundle	3 Bundles	$58	$174	Caps 69 linear ft of roof ridge and hips
T-Style Aluminum Drip Edge Flashing10 ft lengths, painted aluminum/galvanized steel, 1.5" face	20 Pieces	$12	$240	Protects 198 linear ft of fascia and rakes
Electro-Galvanized Coil Roofing Nails (1-1/4")11-gauge, 3/8" head, smooth shank for standard pneumatic roofers	3 Boxes (25 lb)	$42	$126	58 lbs total (approx 4-6 nails per shingle per IRC code)

Geometric Pitch & Area Calculation Breakdown

Area Equations:

Ground Footprint = 1800 sq ft

Eave Overhang Allowance (8%) = +144 sq ft

Adjusted Footprint = 1944 sq ft

Pitch Multiplier (4:12) = √(1 + (4/12)²) = 1.054

True Surface Area = 2049 sq ft

Waste & Packaging Conversion:

Waste Factor Buffer (10%) = +205 sq ft

Total Coverage Area = 2254 sq ft

Roofing Squares = ⌈2254 / 100⌉ = 23 Squares

Shingle Bundles = 23 × 3 = 69 Bundles

Frequently Asked Questions: 1800 Sq Ft (4:12) Roofing

How many squares of shingles do I need for a 1800 sq ft house with a 4:12 pitch roof?

For a 1800 sq ft ground footprint with a 4:12 pitch (pitch multiplier 1.054) and standard 12" overhangs, the true slope surface area is approximately 2049 sq ft. Adding a 10% waste factor for hips, ridges, and valley cut-offs, you will need exactly 23 roofing squares (69 bundles of shingles).

How many bundles of shingles are in a square?

Standard architectural (laminated) shingles and 3-tab asphalt shingles are packaged at 3 bundles per roofing square (100 sq ft). For this 1800 sq ft roof requiring 23 squares, you need to order 69 bundles.

What is the pitch multiplier for a 4:12 roof?

The geometric pitch multiplier for a 4:12 roof is 1.054. This means for every 100 square feet of flat horizontal ceiling or house footprint, the pitched roof surface area expands to 105 square feet.

How much underlayment do I need for 23 squares?

You need 6 rolls of synthetic underlayment (each covering 400 sq ft usable) or 11 rolls of traditional #30 asphalt felt (each covering 200 sq ft). We also recommend 2 rolls of self-adhering ice & water shield for eave ice-dam protection.