onlinecalculator.me

Free online roofing calculator

Roofing material is sold by the square (100 sq ft of sloped surface). Enter your roof footprint and pitch to get sloped area, bundle count, ridge cap, and nails needed.

About this calculator

How to use

  1. Enter roof length and width (the flat footprint).
  2. Select the roof pitch from the dropdown.
  3. Choose architectural or 3-tab shingles.
  4. Set the waste factor (10% for a simple gable).
  5. Read sloped area, squares, and bundle count.

Formulas

pitchFactor = sqrt(1 + (rise/run)²)
  e.g. 6/12 → sqrt(1 + 0.5²) = sqrt(1.25) ≈ 1.118

baseSqFt    = roofLength × roofWidth
slopedSqFt  = baseSqFt × pitchFactor

squares     = slopedSqFt × (1 + waste/100) / 100

bundles     = ceil(squares × bundlesPerSquare)
  3-tab:           3 bundles/square
  architectural:   4 bundles/square

ridgeLength ≈ roofWidth / 2
ridgeBundles = ceil(ridgeLength / 35)

nails (lbs) = ceil(squares × 2.5)

Worked example

40 ft × 30 ft roof, 6/12 pitch, architectural shingles, 10% waste:

pitchFactor = sqrt(1 + (6/12)²) = sqrt(1.25) ≈ 1.118
baseSqFt    = 40 × 30 = 1,200 ft²
slopedSqFt  = 1,200 × 1.118 ≈ 1,342 ft²

squares     = 1,342 × 1.10 / 100 ≈ 14.76 squares
bundles     = ceil(14.76 × 4) = 60 bundles

ridge       = 30 / 2 = 15 ft → ceil(15/35) = 1 bundle
nails       = ceil(14.76 × 2.5) = 37 lbs

Notes

  • Measure the flat footprint from the ground using the exterior wall dimensions. The pitch factor does the rest.
  • Order a few extra bundles beyond the estimate; shingles from different lots may not match exactly if you run short mid-job.
  • Drip edge runs along the eaves (roof length × 2) and rakes (roof width × 2 × pitchFactor) — order separately.

Frequently asked

What is a roofing square?
One roofing square equals 100 square feet of actual roof surface — the sloped area, not the flat footprint. A 1,200 sq ft footprint at a 6/12 pitch becomes about 1,342 sq ft of sloped area, or roughly 13.5 squares before waste.
How does roof pitch affect the material quantity?
Pitch is expressed as rise over run (e.g., 6/12 means 6 inches of rise for every 12 inches of horizontal run). The pitch factor = sqrt(1 + (rise/run)²). A 6/12 pitch has a factor of about 1.118, meaning the sloped area is 11.8% larger than the flat footprint.
How many bundles of shingles per square?
Standard 3-tab shingles come 3 bundles per square. Architectural (dimensional) shingles are heavier and thicker — they come 4 bundles per square. The calculator uses the correct bundle count for the shingle type you select.
What waste factor should I use for roofing?
10% is standard for a simple gable roof with few penetrations. Add to 15% for hip roofs, multiple valleys, skylights, or complex ridgelines.
How much ridge cap do I need?
Ridge cap shingles cover 35 linear feet per bundle. The calculator estimates the ridge length as half the roof width for a standard gable, then divides by 35 and rounds up.
How do I share my roofing calculation?
Click Share for the plain page URL, or Share with my numbers to embed your roof dimensions and pitch in the URL.