Roofing Calculators
Turn a building footprint and a roof pitch into real roof area, then into squares, bundles and underlayment. Includes a pitch calculator that converts between rise-over-run, angle in degrees and slope factor.
Choose a calculator
Roof Pitch Calculator
Free roof pitch calculator: convert between rise-over-run, degrees, percentage slope and the slope multiplier used to turn footprint into roof area.
Roofing Calculator
Free roofing calculator: turn building footprint and pitch into true roof area, squares, and material cost.
Shingle Calculator
Free shingle calculator: get bundles, squares, starter strip, ridge cap and nails from your roof area and pitch.
Footprint area is not roof area
A sloped roof is always larger than the ground it covers, and the difference is bigger than most people guess. The slope factor for a 6/12 pitch is 1.118, so a 1,500 sq ft footprint is a 1,677 sq ft roof. At 12/12 the factor is 1.414 — over 40% more material than the footprint suggests. This is the single most common estimating error on a roof, and it is why the calculators here ask for pitch before they give you an area.
Squares, bundles and waste
Roofing is sold by the square, which is 100 square feet. Most architectural shingles come three bundles to the square; some heavier profiles are four. Waste runs 10% on a simple gable and 15% or more on a hip roof, because every hip and valley means cutting. Starter strip, ridge cap, and underlayment are ordered separately, and the calculator lists them alongside the field shingles so nothing gets missed on the order.
Frequently asked questions
How do I calculate roof area?
Measure the building footprint, then multiply by the slope factor for your pitch. Enter both above and the calculator does it, including overhangs.
What is roof pitch?
The vertical rise in inches over 12 inches of horizontal run. A 6/12 pitch rises 6 inches per foot, which is about 26.6 degrees.
How many bundles of shingles are in a square?
Three for most architectural and three-tab shingles. Heavier designer profiles can be four or five — check the bundle.
How much waste should I allow for roofing?
Ten percent on a simple gable roof, fifteen percent or more on hip roofs and anything with dormers or valleys.
Is it safe to measure a roof myself?
Working at height is genuinely dangerous. Measure the footprint from the ground where you can, and have a roofer verify anything you would need a ladder for.