What panel width should I enter?

The coverage (exposed) width, not the nominal width. Exposed-fastener panels are usually sold by a 36-inch coverage width; standing-seam panels are narrower (typically 12–18 inches of coverage). It's printed in the product's specs.

How long should the panels be?

Ideally the full eave-to-ridge length of each roof plane, so there are no horizontal seams to leak. That's the sloped distance up the roof, not the footprint depth — if you only have the footprint, get the slope length from the roof area calculator first. Order panels cut to that length where you can rather than overlapping shorter ones.

Does this include trim and fasteners?

No — ridge cap, eave and rake trim, closures, and screws are separate. This counts the field panels; add the trim by the linear foot of ridge, eaves, and rakes.

Metal Roof Calculator

Metal roofing goes on in panels, each covering its exposed width times its length. Enter your roof area and the panel size for the number of panels, with a waste allowance.

Panels

52panels

Roofing squares: 17 squares
Total panel length: 624 linear ft

How these numbers are worked out

The formula

Panels = roof area × (1 + waste) ÷ panel coverage, rounded up. Panel coverage is the exposed width (after the side overlap) times the panel length. Use the exposure width, not the nominal width — a panel sold as 36 inches covers a bit less once it laps the next one.

Constants and sources

Panels = roof area × (1 + waste) ÷ (exposure width × length), rounded up. Panel dimensions are product-specific (use the coverage/exposure width) — entered, not assumed. Roofing square = 100 sq ft.

How it was checked

Last reviewed June 16, 2026. Before this calculator was published, its formula, constants and worked example were checked in a separate, AI-assisted review that redid the arithmetic and tested the factual claims; the site owner then approved it for publishing. No engineer or tradesperson reviews these pages. Where a figure depends on the product (a density, a coverage rate, a bag size), it is either an input you can change above or a fixed planning value stated on this page, so check it against your product's label or your supplier.

Spot a wrong number or an outdated figure? Send a correction.

Worked example

1,700 sq ft of roof with 36-inch (3 ft) × 12 ft panels covering 36 sq ft each, 10% waste: 1,700 × 1.10 ÷ 36 ≈ 52 panels (17 squares).

FAQs

What panel width should I enter?: The coverage (exposed) width, not the nominal width. Exposed-fastener panels are usually sold by a 36-inch coverage width; standing-seam panels are narrower (typically 12–18 inches of coverage). It's printed in the product's specs.
How long should the panels be?: Ideally the full eave-to-ridge length of each roof plane, so there are no horizontal seams to leak. That's the sloped distance up the roof, not the footprint depth — if you only have the footprint, get the slope length from the roof area calculator first. Order panels cut to that length where you can rather than overlapping shorter ones.
Does this include trim and fasteners?: No — ridge cap, eave and rake trim, closures, and screws are separate. This counts the field panels; add the trim by the linear foot of ridge, eaves, and rakes.