Roofing Shingles Calculator
Estimate asphalt shingles in roofing squares (100 sq ft) and bundles. Enter the actual roof-surface area - measured along the slope, not the ground footprint.
Roofing Shingles calculator
How it's calculated: Roof length ft × slope width ft = square feet; add 10% waste and divide by 100 for roofing squares. Three bundles cover one square.
How to estimate roofing shingles
- Measure the sloped roof area, not the building footprint. Multiply footprint by a pitch factor (~1.05-1.25) if estimating from the ground.
- Three bundles cover one square for most architectural shingles. Add 10% for hips, valleys and starter.
- Order matching ridge cap, starter strip, underlayment and drip edge alongside the field shingles.
- Budget for tear-off: dumpster, disposal fees and the chance of rotten decking that needs new plywood before shingles go on.
- Be honest about height and pitch - steep or multi-story roofs are dangerous, and roofing is one of the most commonly hired-out trades for good reason.
Frequently asked questions
How many bundles of shingles in a square?
Three bundles per square for standard architectural shingles.
What is a roofing square?
A square is 100 square feet of roof surface - the standard unit for ordering and pricing roofing.
How do I estimate roof area from the ground?
Measure the building footprint and multiply by a pitch factor: about 1.05 for low slopes, 1.12 for a common 6/12 pitch, up to 1.25 for a steep 9/12. A 30x40 footprint at 6/12 is roughly 1,350 sq ft - call it 13-14 squares before waste.
How much waste should I add for shingles?
10% covers a simple gable roof. Go to 15% for roofs with hips, valleys and dormers - every cut line eats shingles.
Can I shingle over the old layer?
Many codes allow one overlay, but tear-off is usually worth it: it reveals bad decking, lays flatter, weighs less and typically carries a better warranty. Two existing layers means tear-off is mandatory.
What else do I need besides shingles?
Underlayment, drip edge, starter strip, ridge cap, nails and any flashing or pipe boots being replaced. These add meaningfully to the bill, so price them alongside the field shingles.