Metal Roofing Calculator
Count metal roofing panels from your roof size and pitch — standing seam, corrugated or 3-ft rib panels — plus ridge cap, trim and the screws or clips to fasten it.
Panels counted the way metal roofing is sold
Metal roofing is not bought by the square foot of roof — it is bought as panels of a fixed coverage width, cut to the slope length. So the count runs the way an order actually gets written: how many panel widths fit along the eave, per slope, and how long each panel must be. The slope length comes from the pitch: half the building width (the run) plus the eave overhang, stretched by the slope factor — the same factor the roofing calculator uses for shingles.
Slope factor = √(1 + (pitch ÷ 12)²) · Panel length = (run + overhang) × factor · Panels per slope = eave length ÷ coverage width, rounded up
Example: a 40 × 30 ft building at a 6/12 pitch with a 1 ft overhang: the factor is 1.118, each slope runs 17.89 ft, the roof covers 1,431 sq ft, and 3-ft rib panels work out to 28 panels (14 per slope), 5 pieces of ridge cap, and about 1,575 screws — 7 boxes of 250 — at the standard one screw per square foot.
The three panel families cover at their working widths: 3-ft rib panels at a full 36 in, corrugated at 24 in after the side lap, and standing seam at 16 in between seams. Exposed-fastener roofs are screwed at roughly one screw per square foot of roof when the maker's pattern (screws in the flats or ribs at every purlin row) is averaged out; standing seam instead clips to the deck, at about one clip every 18 in up each seam. Panel counts are exact — you cannot buy a tenth of a panel — so the waste allowance rides on the ridge pieces, trim and fasteners, where the cutting and the dropped screws actually happen. Order panel lengths a touch long if your supplier allows it: a panel can be trimmed at the eave, it cannot be stretched at it.
Frequently asked questions
How many screws does a metal roof need?
The planning figure for exposed-fastener panels is about one screw per square foot of roof — the average of the maker's fastening pattern over purlin rows and panel laps. Steeper roofs and high-wind zones call for denser patterns; the panel maker's own chart governs your roof, and the calculator's allowance leaves room in the count.
Standing seam vs exposed fastener — which is better?
Standing seam hides every fastener under the seam, so there are no screw holes through the panel to age — it costs more per square and installs slower. Exposed-fastener rib and corrugated panels are the budget workhorses: faster, cheaper, and the screws want a look (and eventually new washers) on a decades timescale, not a yearly one.
Can metal roofing go over old shingles?
Often, yes — many codes allow one layer of shingles under metal, usually over furring strips or a slip sheet. It saves the tear-off, but soft or curled shingles telegraph through thin panels, and the local code has the final word. Confirm locally before planning on it.
What gauge metal roofing should I buy?
Residential panels are usually 29 or 26 gauge (the lower the number, the thicker the steel). 29 gauge serves most homes; 26 is the usual upgrade for hail country, long panel runs and standing seam. Coastal roofs step up to aluminum or Galvalume coatings against salt air.
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