Divide the roof width by the panel coverage width — usually 36 inches for exposed-fastener panels, not the 38-inch nominal width — and round up, then double it for both slopes. Panel length is the eave-to-ridge rafter length, not the horizontal run.
The Metal Roof Calculator estimates panels, fasteners, ridge cap, eave trim, and total project cost for a standing-seam or corrugated metal roof. Enter your roof dimensions, pitch, panel width (typically 24" or 36"), and material type (galvalume, painted steel, aluminum, copper) and the tool returns panel count, fastener count, trim length, and a full cost breakdown. Metal roofs cost more upfront than asphalt but last 50+ years and qualify for energy-efficiency credits.
Metal roofing is sold by the panel. Panel count comes from the roof width divided by the panel coverage width, and panel length from the eave-to-ridge run, which is the rafter length rather than the horizontal distance.
| Roof footprint | Sloped area | 36 in panels | Panel length needed |
|---|---|---|---|
| 1,000 sq ft | 1,118 sq ft | 28 | 14 ft |
| 1,500 sq ft | 1,677 sq ft | 34 | 16.8 ft |
| 2,000 sq ft | 2,236 sq ft | 34 | 22.4 ft |
| 2,500 sq ft | 2,795 sq ft | 34 | 28 ft |
| 3,000 sq ft | 3,354 sq ft | 40 | 28 ft |
Most exposed-fastener panels cover 36 inches of the 38 inch sheet once the sidelap is taken out. Standing seam is usually 16 or 18 inches of coverage, so panel counts roughly double.
Exposed-fastener panels are screwed straight through the face into the deck or purlins. They are much cheaper, they are what most agricultural and outbuilding roofs use, and the screws are a maintenance item — the neoprene washers need checking every few years and the roof will usually need refastening once in its life.
Standing seam hides the fasteners under clips inside the seam, so there is nothing to degrade in sunlight and nothing to back out. It costs substantially more, needs a narrower panel and therefore roughly double the panel count, and it allows the panel to expand and contract along its length, which matters on long runs.
Divide the roof width by the panel coverage width — usually 36 inches for exposed-fastener panels — and round up, then double it for both slopes. Panel length is the eave-to-ridge rafter length, not the horizontal run.
A 38 inch panel typically covers 36 inches once the sidelap is taken out. Always calculate on coverage width or you will come up short.
Roughly 80 per square for exposed-fastener panels, screwed on the flat next to the rib rather than through the rib itself.
Exposed-fastener panels generally need 3/12 or steeper. Standing seam with sealed seams can go as low as 1/4 in 12 on some systems — check the specific product.