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Metal Roof Calculator: Panels and Roof Area

Work out how many metal roof panels you need from the eave length, slope length and panel coverage, plus the code's minimum slopes for metal roofs.

Updated
Reading time2 min
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Key takeaways

  • Panels per plane = eave length ÷ panel coverage width, rounded up.
  • Use the panel's coverage width, which is narrower than its overall width on many panels.
  • Minimum slope depends on the system, from 1/4:12 for standing seam to 3:12 for lapped panels without sealant.

Enter the eave length and the distance from eave to ridge for one roof plane, along with the number of matching planes. A simple gable roof has two.

  • Panels28 panels14 panels per plane, each about 15 ft plus any overhang
  • Roof area1,200 sq ft12 squares

Nothing you enter leaves your browser. For simple rectangular planes. Coverage varies by panel, so use the figure for yours. Hips, valleys and trim need a supplier's takeoff.

Show the math with your numbers
  1. Per plane: 480 in ÷ 36 in, rounded up to 14
  2. Panels: 14 × 2 = 28
  3. Area: 40 × 15 × 2 = 1,200 sq ft
What if: panel coverage
Panel coveragePanels
12 in80 panels
16 in60 panels
24 in40 panels
36 in (yours)28 panels

The default coverage of 36 inches is only an example. Use the figure for your panel, which the manufacturer or supplier can give you.

How the calculator works

  1. Panels per plane: eave length in inches ÷ panel coverage, rounded up
  2. Total panels: panels per plane × number of planes
  3. Area: eave length × eave-to-ridge length × number of planes
  4. Squares: area ÷ 100

Worked example

A gable roof with 40-foot eaves, 15 feet from eave to ridge, using panels that cover 36 inches:

  • Per plane: 480 ÷ 36 = 13.3, which rounds up to 14 panels
  • Two planes: 28 panels, each about 15 feet plus any overhang
  • Area: 40 × 15 × 2 = 1,200 square feet, or 12 squares

To find the eave-to-ridge length, use the rafter length calculator.

Minimum slope for metal roofs

Section R905.10.2 of the 2021 International Residential Code (IRC) sets these minimums for metal roof panels:

System Minimum slope
Lapped, non-soldered seams, no lap sealant 3/12
Lapped, non-soldered seams, with lap sealant 1/2:12
Standing seam 1/4:12

Your local code and the panel's instructions may differ, so check both. To find your slope, see how to measure roof pitch.

What this calculator doesn't cover

  • Hips, valleys and dormers: angled cuts create waste that depends on the layout, so ask for a supplier's takeoff.
  • Trim and fasteners: ridge caps, eave and rake trim, closures, underlayment and fasteners are separate.
  • Panel length: long panels can be hard to ship and handle, so ask your supplier about length limits and end laps.

How coverage changes the panel count

For one 40-foot eave:

Panel coverage Panels
12 in 40
16 in 30
24 in 20
36 in 14

So check the exact product. Narrow standing-seam panels and wide lapped panels give very different counts for the same roof.

Frequently asked questions

What's the difference between panel width and coverage?

Panels overlap or interlock, so the width each one covers can be less than its overall width. Calculate with coverage.

How do I measure a hip roof for metal panels?

Hip planes are triangles or trapezoids, so this simple panel count won't fit. Use the roof area calculator for the area, then get a takeoff from your supplier.

Can metal roofing go on a low-slope roof?

The 2021 IRC allows standing-seam systems down to 1/4:12, as long as the system and local rules allow it.

Sources

We use primary sources where we can: building codes, federal rules and manufacturer documents. Read our editorial standards.