How to Measure Your Roof (Footprint, Pitch, Total Area)
Measure length and width from the ground, including overhang. Footprint area = length × width. True roof area = footprint × the pitch area multiplier (the same √(rise² + run²) ÷ run factor used on the Roof Pitch Calculator). For a cross-gable or extra wing, add another section and the calculator sums the areas.
Roof Pitch Area Multiplier Table
These multipliers come from the shared pitch function — they are not a second table. A 4/12 roof is about 5% larger than its footprint; a 12/12 roof is about 41% larger.
| Pitch | Multiplier | Pitch | Multiplier |
|---|
Finding Roof Size in Squares
A roofing square is 100 sq ft of actual roof surface — the unit most US suppliers quote. Divide true roof area by 100 and round up to the next full square. UK mode reports m² as the working unit because “square” is not the usual UK quote, but the same area math still applies.
Shingle Bundles: How Many You Need
A typical asphalt bundle covers about 33.3 sq ft, so three bundles make one square. Bundles = squares × 3. That count is for 3-tab and architectural asphalt only. Wood, metal, tile, and slate are sold by panel, piece, or pallet — the calculator shows a note instead of a fake bundle number.
Felt/Underlayment: Rolls Needed
A 15 lb felt roll covers about 4 squares (400 sq ft). A 30 lb roll covers about 2 squares (200 sq ft) and is the usual pick for asphalt. Tile roofs often need 50 lb felt. Synthetic underlayment is lighter; coverage is similar on paper but always check the manufacturer’s roll size.
Nails and Fasteners: How Many You Need
3-tab shingles: about 80 shingles per square × 4 nails = 320 nails per square. Architectural shingles can take up to 480 nails per square. Tile, slate, and standing-seam metal use clips or hidden fasteners — do not order shingle nails for those systems without the manufacturer’s schedule.
Drip Edge, Fascia & Other Materials
Drip edge and fascia are sold by the linear foot. For a simple rectangle, perimeter ≈ 2 × (length + width) per section. Complex roofs can skip that guess and type a measured perimeter. Ice-and-water membrane, ridge cap, and ventilation are extra line items your supplier should quote from the same square count.
Why You Should Order 5–10% Extra
Cuts at hips, valleys, and rakes eat material, and tape-measure error adds up. The calculator lists a 5–10% overage as a separate “order this many extra” line so the base count stays honest. Lean toward 10% on special-order tile, slate, or metal that takes weeks to restock. Permits and HOA color boards are not in this quantity math — ask the building department before you buy.
Frequently Asked Questions
How do I calculate how much roofing material I need?
Measure your roof's length and width from the ground (including overhang), multiply to get the footprint area, then multiply by your pitch's area multiplier to get true roof area. Divide by 100 to get squares, then convert squares to bundles, felt rolls, and nails using standard coverage rates.
What is a "square" in roofing?
A square is 100 square feet of roof area — the standard unit contractors use to quote roofing projects and materials.
How many bundles of shingles are in a square?
Standard asphalt shingle bundles cover about 33.3 sq ft each, so it takes 3 bundles to cover one square (100 sq ft).
How much does roof pitch affect the material I need?
Steeper roofs have more actual surface area than their footprint suggests — a 4/12 pitch adds about 5% more area, while a 12/12 pitch adds over 41% more area than the flat footprint.
How many rolls of felt do I need for my roof?
A roll of 15lb felt covers about 4 squares (400 sq ft); a roll of 30lb felt covers about 2 squares (200 sq ft). Most roofs use 30lb felt, though tile roofs often require 50lb.
How many nails does a roofing job need?
Standard 3-tab shingles need about 320 nails per square (4 nails per shingle, 80 shingles per square); architectural shingles can need up to 480 nails per square.
How much extra material should I order?
Order 5–10% more than your calculated total to cover cutting waste and measurement error — more for special-order materials like tile or slate that have long lead times.
Do metal or tile roofs use bundles like asphalt shingles?
No — metal panels, tile, and slate are sold and measured differently (by panel, piece, or pallet). This calculator's bundle count applies to asphalt shingles only.
Get free quotes from local roofing contractors
This tool sizes materials for a DIY takeoff. If you want a crew, get 2–3 local quotes before you order a pallet.