Metal Roofing Calculator
Calculate how many metal roofing panels, screws, closure strips and ridge cap you need from the eave length, panel length and panel coverage width, with waste.
By CalcBuilt Editorial TeamUpdated September 10, 2026Formulas checked against manufacturer specs, see how we calculate.
Results
- Metal panels to buy
- 30 panels
- 14 per side x 2 sides plus 5% waste; 36 in coverage x 18 ft long
- Total panel length
- 540 ft
- 1,440 sq ft of roof surface, 14.4 squares
- Screws
- 1,152 screws
- Metal-to-wood screws with sealing washers, driven in the flat next to the rib on exposed-fastener panels
- Closure strips
- 80 ft
- Foam closures along every eave; buy the same length again for under the ridge cap
- Ridge cap (gable roof)
- 40 ft
- 4 pieces at 10 ft each, plus rake trim for the gable ends; a single-slope shed roof needs eave trim instead
Metal Roofing formula
Panels per side = Eave length (in) / panel coverage width, rounded up
Panels to buy = Panels per side x sides x (1 + waste %)
Screws = Eave x panel length x sides / 100 x screws per square
Closure strip = Eave x sides; Ridge cap = Eave lengthWorked example
A 50 ft long gable roof with 14 ft rafters, 24 in standing seam panels and 5% waste: 50 x 12 = 600 in / 24 = 25 panels per side, x 2 sides = 50, x 1.05 = 52.5, so buy 53 panels of 14 ft, which is 742 linear ft of panel. Closure strips: 50 x 2 = 100 ft. Ridge cap: 50 ft, or 5 pieces of 10 ft.
The roof surface is 50 x 14 x 2 = 1,400 sq ft, or 14 squares. Exposed-fastener panels would need 14 x 80 = 1,120 screws; standing seam uses about one clip per foot of seam instead.
Quick reference
| Eave length | 36 in panels | 24 in panels | 16 in panels |
|---|---|---|---|
| 20 ft | 7 | 10 | 15 |
| 30 ft | 10 | 15 | 23 |
| 40 ft | 14 | 20 | 30 |
| 50 ft | 17 | 25 | 38 |
| 60 ft | 20 | 30 | 45 |
| 80 ft | 27 | 40 | 60 |
How to calculate metal roofing panels
Metal panels run from eave to ridge, so you need two measurements: the length of the eave and the length of the slope from eave to ridge. Divide the eave length in inches by the net coverage width of the panel, 36 inches for most corrugated and ribbed panels, and round up to whole panels. Do that for each side of the roof and add 5 percent for a simple gable, more if valleys or hips require angled cuts.
Order panels the slope length plus 1 to 2 inches of eave overhang, measured at both ends of the roof, since an out-of-square roof can differ by an inch. Suppliers roll-form to the inch up to about 40 feet, lead time typically 1 to 3 weeks, and custom lengths are not returnable. On a longer slope plan a 6 inch end lap over a purlin with butyl tape.
Screws, closures and trim
Exposed-fastener panels take #10 x 1-1/2 inch screws with a bonded washer, 2 inch through old shingles, on a 24 inch grid, about 80 per square. MBCI and McElroy put them in the flat beside the major rib on PBR and R-panel; some corrugated and 5V makers want the rib, so follow the panel's sheet. Set the clutch so the washer just bulges to the edge of the head. Stitch screws go every 12 to 20 inches along side laps over butyl tape. Standing seam hangs on clips, one every 12 to 24 inches per seam.
Closures must match the panel profile: inside closures at the eave, outside or vented closures under the ridge cap. Ridge cap comes in 10 foot lengths; add rake trim, eave trim and sidewall or endwall flashing where the roof meets a wall. IRC R905.10.2 minimum slopes: 3/12 for lapped panels without lap sealant, 1/2 in per foot with it, 1/4 in per foot for standing seam. Use a high-temp synthetic underlayment. A 40 foot steel panel grows about 5/16 inch over a 100 degree swing, so runs that long need floating clips.
What this calculator leaves out
Pipe boots made for metal, butyl tape at every lap, underlayment, and purlins or a slip sheet over old shingles. Snow guards in snow country, touch-up paint for cut edges, and a flatbed delivery fee, typically $75 to $250. Sweep filings off the panels the same day; they rust into the finish.
Mistakes that cost money
- Ordering panels from one measurement: the slope length differs end to end on an out-of-square roof; measure both ends, since custom-cut panels are not returnable.
- Cutting panels with an abrasive blade: it burns the coating and the hot swarf rusts into the finish; use shears or a nibbler.
- Overdriven screws: the washer squeezes out past the head and splits; set the driver clutch so the rubber just bulges to the edge.
- Universal foam closures on a PBR profile: the gaps let wind-driven rain and wasps under the ridge; buy closures cut for the exact panel profile.
- Running exposed-fastener panels over 40 ft: steel grows 5/16 in per 40 ft over a 100 degree swing and wallows the holes; go standing seam.
- Screws through the rib of a PBR panel: the washer rocks and leaks; MBCI and McElroy specify the flat beside the major rib.
Key facts
- Corrugated, R-panel and PBR panels have a net coverage of 36 in even though the sheet is about 38 in wide, because one rib overlaps the next panel.
- Standing seam panels are commonly 12, 16, 18 or 24 in wide and are fastened with hidden clips, so there are no exposed screws in the field.
- Plan on about 80 screws per square (100 sq ft) for exposed-fastener panels on 24 in purlin spacing.
- Metal panels weigh about 0.6 lb per sq ft for 29 gauge ribbed panels and up to 1.5 lb for 24 gauge standing seam, a third to half the weight of asphalt shingles, and are usually cut to order in lengths up to 40 ft or more.
- 29 gauge is the common residential thickness for agricultural style panels; 26 and 24 gauge are heavier and used for standing seam and commercial work.
Frequently asked questions
How many metal roofing panels do I need for a 40 ft roof?
With 36 in coverage panels, 40 ft x 12 = 480 in / 36 = 13.3, so 14 panels per side, or 28 for a gable roof before waste.
How many screws per sheet of metal roofing?
About 80 screws per 100 sq ft. A 3 ft by 12 ft panel is 36 sq ft, so about 29 screws per panel on 24 in purlin spacing.
Can I install metal roofing over my old shingles?
Usually yes, over one layer. IRC R908.4 allows a roof recover over a single layer of asphalt shingles if the deck is not water-soaked or rotten, and prohibits it over two or more layers. Put a synthetic underlayment or slip sheet between the shingles and the metal so the granules do not chew the paint. Use 2 in screws so they reach the deck. Some manufacturers and jurisdictions require 1x4 purlins instead; check the panel's installation sheet and your building department.
How much overhang should metal roofing have?
About 1 to 2 in past the fascia or drip edge at the eave so water drips into the gutter. Rakes are usually covered by rake trim with little or no overhang.
Sources and references
- PBR metal roof and wall panel product page (MBCI)
- R-Panel exposed fastener roofing panel product page (McElroy Metal)
- Metal Roof Installation Manual (Metal Construction Association)
- Chapter 9 Roof Assemblies, 2021 IRC (ICC)
Next steps for this project
The usual order for a roofing & siding project. See all roofing & siding calculators.
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Results are estimates based on standard formulas and typical product specifications. Confirm quantities with your supplier and local code before ordering.