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Metal Roofing Calculator

4run 12pitch 4/12 · slope factor 1.054
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1,264.91 sq ft of roof

12.65 squares (roof area 1264.91 sf = footprint × 1.05 slope factor); 1391.4 sf with 10% waste.

Metal panels: 14 runs per side × 2 sides = 28 panels at 15.81 ft each (eave ÷ net 36″ coverage; using gross width short-orders you about 5-8%).

  • Sloped area = footprint × √(1+(rise/12)²) = 1200 × 1.05. Pure geometry: include eave/rake overhangs in your footprint or this understates.
  • Waste: 10% for simple gable (JLC convention). Waste is a range by design; cut-up roofs can exceed 15%.
  • Footprint estimation fails on complex plans (dormers, turrets, intersecting gables); measure each roof plane there instead.
  • A 4/12-vs-8/12 pitch mistake is a 14% area error: verify pitch, don't guess it.
  • Panel math assumes a simple gable (two rectangular planes). Hips, valleys, and dormers need per-plane takeoff.

Why This One Is Different

Metal roofing math has one trap the shingle world doesn't: panel coverage width. A '38-inch' corrugated panel covers 36 inches after side laps, and running the gross width through your area math shorts the order by 5% before you've cut a single panel. This calculator gets the roof area right first (footprint times the pitch slope factor, pure trigonometry), and then talks panels the way suppliers actually sell them: by coverage width, in whole panels, cut to your eave-to-ridge length.

Where the Numbers Come From

  • Guess your pitch instead of measuring it and your area estimate can be off by double digits: sloped roof area = horizontal footprint × √(1+(rise/12)²), where a 4/12 roof multiplies by 1.054, an 8/12 by 1.202, and mixing those two up is a 14% area error. Source: slope-factor geometry, verified against Roof Online pitch table / JLC field guide
  • Order by the panel's real coverage width, not the width printed on the label, or you'll come up short: panel takeoff divides area by coverage width (net after side lap), not gross panel width, the classic 5-8% short-order mistake. Source: metal panel manufacturer installation guides (product-specific spec)
  • Metal roofs are commonly estimated panel-by-run rather than by square: count runs = roof width ÷ coverage width, panel length = eave-to-ridge + overhang. Source: supplier estimating practice (True Metal Supply-class calculators)

More Questions

Does this work for standing seam?

The area math is identical; coverage width differs (commonly 12-18" for standing seam vs ~36" corrugated). Use your panel's spec sheet coverage, and expect trim/flashing to be quoted separately.

Related Calculators

Formulas, waste factors, and cost models on this page follow the sourced conventions on our methodology page. Estimates only; verify with your supplier and local code.