What Is a Roofing Square?
One roofing square = 100 square feet of roof surface — the unit every quote, bundle count, and warranty is written in. Architectural shingles usually come 3 bundles per square (some brands 4), so a 13-square roof is roughly 39–52 bundles plus waste. Underlayment rolls cover about 4 squares each; starter strip and ridge cap are sold separately.
Why Pitch Multiplies the Area
Your roof is bigger than your house’s footprint because it slopes: a 6/12 pitch (6 inches of rise per foot of run) stretches each foot of floor into 1.118 feet of roof — that is sqrt(1 + (6/12)²), the Pythagorean theorem at work (see our Pythagorean calculator for the interactive version). Steeper is bigger: at 12/12, the roof surface is 41% larger than the footprint below it. Measuring each roof plane directly is more accurate than footprint math on complex roofs — use this estimate for simple gables and material sanity checks.
Frequently Asked Questions
How many bundles of shingles do I need for a 2,000 sq ft house?
It depends on pitch. A 2,000 sq ft footprint at low slope is about 20.6 squares ≈ 62 bundles; at 6/12, about 22.4 squares ≈ 67 bundles. Add 10–15% waste and you are ordering roughly 69–77 bundles — plus starter strip, ridge cap, and underlayment rolls (1 per 4 squares).
How long do asphalt shingles last?
Three-tab shingles typically last 20–25 years; architectural (dimensional) shingles 30–50 in moderate climates. Real-world life is driven by ventilation, installation quality, and climate — a poorly ventilated attic cooks shingles from below, and hail or constant 12/12 sun can halve the calendar. Warranties run 25 years to lifetime, but prorated payouts rarely cover replacement labor.
Does a steeper roof cost more to shingle?
Yes, twice. Material: the pitch multiplier grows the surface — 12/12 is 41% more roof than the footprint below it. Labor: walkable pitches (up to about 7/12) are standard rates; steeper roofs need staging, harnesses, and crews that charge for it, often 1.5–2× per square. Both effects are already visible in the calculator when you change pitch.