How many metal roof panels do I need?

Divide the roof length by the panel's coverage width, round up, and multiply by the number of roof planes. The example roof is 38 ft long (36 ft plus a 12 in overhang at each end), so 12.67 panels of 36 in coverage is 13 on each side, and 26 in all for a gable roof. A last panel is usually ripped to width, so the count always rounds up.

What is the coverage width of a metal roof panel?

It is what one panel covers after its side lap or seam is overlapped, and it is less than the overall width. R-panel, AG panel and Classic Rib profiles are sold with 36 in of coverage (a sheet of about 37 3/4 in overall); standing seam panels are commonly 16 in, for example Berridge's Zee-Lock, with 12 and 18 in profiles also made. This calculator offers 36 in and 16 in. If your panel differs, divide the roof length by its coverage width yourself.

How long should I order the panels?

Panels run in one piece from the eave to the ridge. The length is the run plus the overhang, times the pitch factor, plus the hang past the eave edge, rounded up to the inch: 16' 10 1/4" for the example, so 16' 11". Makers roll panels to length, commonly up to 40 ft, so one order covers most house roofs. Check with your supplier about set-back at the ridge, and about the cut length for a roof over 40 ft.

How far should metal panels overhang the eave?

Enough for water to drip clear of the fascia instead of running back under the panel. Trade guides give about 1 in over a gutter and 2 to 3 in without one, and Texas wind-product evaluations limit the projection to 2 in past the fascia for the R-panel installations they tested. Follow your maker's manual: this calculator adds the figure you enter to the panel length.

How many screws does a metal roof need?

For exposed-fastener panels the page estimates 115 per square (100 sq ft), the figure Berridge lists for its R-panel; the example roof comes to about 1,466 screws. Other profiles and patterns need more (Berridge lists up to 155 per square for some), high-wind zones add fasteners, and the maker's pattern and spacing for your panel and purlin or deck rule. Buy extra: screws drop. Standing seam panels clip down at the maker's spacing and need no figure here.

How much ridge cap do I need?

Ridge cap is counted along the roof length. A usual piece is 10 ft 6 in long and covers 10 ft of ridge once the 6 in lap is allowed, so the 38 ft ridge of the example takes 4 pieces. A shed roof has no ridge: the same length of high-side trim goes along the top. Closure strips, eave and rake trim and flashing are bought separately and are not counted here.

What roof pitch can metal panels go on?

Exposed-fastener panels are usually listed for 3/12 and steeper (the AG panel data sheet gives 3/12 as the recommended minimum), and standing seam is used on lower slopes: the IRC (R905.10.2) sets 3/12 for lapped seams without sealant, 1/2 in 12 with lap sealant and 1/4 in 12 for standing seam systems. Slope limits, underlayment and fastening depend on the panel and the maker, so use the data sheet or the supplier for yours. The slope calculator turns an angle or a percent grade into x/12.

Does the calculator handle hips, valleys and dormers?

No. It works a plain gable or shed roof, where every panel is the same length. Hips and valleys need panels cut on a diagonal, with each panel a different length, and a dormer or an addition is its own roof. Work those parts separately with the length and span of each, and ask your supplier to lay out the cut panels.

Do I need underlayment and a permit?

Most manufacturers call for underlayment over solid sheathing and many places require a permit for a re-roof. Underlayment, sealants and closures are not counted here. Check the maker's manual and your local code, and use fall protection: metal roofing is slippery.

Metal Roofing Calculator: How Many Panels and What Length?

A 36 ft long, 28 ft wide gable building with a 6/12 pitch and a 12 in overhang needs 26 panels of 36 in coverage: 13 on each side, since the 38 ft roof length ÷ 3 ft is 12.67, rounded up. Each is ordered 16' 11" long (the 16' 10 1/4" slope length, which includes a 1 in drip past the eave, rounded up to the inch), for 1,320 sq ft of panel over 1,275 sq ft of roof. The ridge takes 4 pieces of ridge cap. Coverage widths and the screw count vary by maker, so check the data sheet for your panel.

Figures based on the sources listed belowUpdated 2026-10-07How we calculate

Roof length along the eave (building length)

Building span (outside of wall to outside of wall)

Spare panels

Exact count (0%)A spare for a cutting mistake or damage (5%, an estimate)Custom

Roof planesA gable is two matching slopes meeting at a ridge; a shed roof is one slope across the whole span. Hip roofs and valleys need panels cut on a diagonal: ask the maker to lay them out.

Roof pitch (rise per 12 in of run, x/12)

A 6 means the roof rises 6 in for every 12 in across. Use the slope calculator if you only have an angle or a percent. Most exposed-fastener panels want at least 3/12.

Panel typeCoverage width is what one panel covers once its side lap or seam is overlapped, not its overall width. Panels vary by maker (standing seam comes in 12 to 18 in), so check the data sheet for yours.

Roof overhang (in)

How far the roof sticks out past the walls, level, at the eaves and the gable ends (rakes). Use 0 if the length and span you entered already include it.

Panel hang past the eave edge (in)

How far the panel sticks out past the eave trim or fascia so water drips clear, measured along the panel. Installers use about 1 in over a gutter and 2 to 3 in without one (check your maker). Added to the panel length.

Price per panel (optional)

Buy 26 panels

439.83 linear ft + 0% waste = 439.83 linear ft

Panels per side (roof length ÷ coverage width, rounded up): 13 panels
Panel length to order (slope length, rounded up to the inch): 16' 11"
Panel area ordered (panels × length × coverage width): 1,320 sq ft
Roof surface covered: 1,275 sq ft
Ridge cap, pieces of 10 ft 6 in (10 ft of ridge each): 4 pieces (≈ 38 ft)
Panel screws, 115 per square (Berridge R-panel estimate): 1,466 screws

How this number is calculated

439.83 linear ft (no waste added) ÷ 16.92 linear ft per panel = 26 panels

Shopping list

Metal roofing screws with neoprene washers
Metal roofing snips (aviation snips)
Panel closure strips (foam)
Butyl tape sealant
Roofing underlayment, synthetic
Roof harness and rope grab kit
Magnetic nut driver (1/4 in or 5/16 in)
Chalk line

Show diagram

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Panels per side by roof length

Roof length ÷ coverage width, rounded up, worked by this calculator. Roof length is the building length plus the overhang at both gable ends. Use the same count for each side of a gable roof.
Roof length along the eave	36 in coverage (R-panel, AG)	16 in coverage (standing seam)
20 ft	7	15
24 ft	8	18
30 ft	10	23
36 ft	12	27
40 ft	14	30
48 ft	16	36
60 ft	20	45

Panel length to order by span and pitch

Gable roof, no overhang, 1 in hang past the eave edge, rounded up to the inch, worked by this calculator. Add the overhang along the slope (the horizontal overhang × the pitch factor) for a roof that has one. Past 40 ft, ask your maker about a lap.
Building span	3/12 pitch	4/12 pitch	6/12 pitch	8/12 pitch	12/12 pitch
20 ft	10' 5"	10' 8"	11' 4"	12' 2"	14' 3"
24 ft	12' 6"	12' 9"	13' 6"	14' 7"	17' 1"
28 ft	14' 7"	14' 11"	15' 9"	16' 11"	19' 11"
32 ft	16' 7"	17' 0"	18' 0"	19' 4"	22' 9"
36 ft	18' 8"	19' 1"	20' 3"	21' 9"	25' 7"
40 ft	20' 9"	21' 2"	22' 6"	24' 2"	28' 5"

Panel figures used here

Published figures for the profiles named; your maker's data sheet rules.
Item	Figure used	Note
R-panel and AG panel	36 in coverage	Exposed fasteners; most makers list a 3/12 minimum slope
Standing seam panel	16 in coverage	Concealed clips; some makers use 12 or 18 in
Panel screws (exposed fastener)	115 per square	Berridge R-panel estimate; other profiles and wind zones differ
Ridge cap	10 ft of ridge per 10 ft 6 in piece	6 in lap between pieces
Panel hang past the eave	1 in default	About 1 in over a gutter, 2 to 3 in without; the field is yours to change

Methodology & assumptions

Enter the building length along the eave (the direction the panels are laid across), the span (outside of wall to outside of wall, across the rafters), the pitch, the overhang and the panel type. The roof length is the building length plus the overhang at each gable end (rake). Panels per side = roof length ÷ the panel's coverage width, rounded up: coverage width is what a panel covers after its side lap or seam is overlapped, 36 in for the R-panel and AG panel profiles and 16 in for the standing seam panel used here (standing seam is made in about 12 to 18 in widths, so check yours). The run is half the span for a gable (two planes) or the whole span for a shed roof (one plane), plus the overhang; the slope length is that × the pitch factor √(1 + (rise ÷ 12)²) plus the panel's hang past the eave edge. The panel length to order is the slope length rounded up to a whole inch. Panels run in one piece from eave to ridge, so every panel is the same length; this calculator takes the top of each panel as the ridge line, and the installer sets any set-back at the ridge. Total panels = panels per side × planes, plus the spares you pick, rounded up. Panel area is panels × length × coverage width, what you buy; the roof surface covered is the true roof area under them. Ridge cap is counted on the roof length at 10 ft of ridge per piece, the usual 10 ft 6 in piece with a 6 in lap. The screw estimate is shown only for the exposed-fastener type, at 115 per square (100 sq ft) of roof, the figure Berridge publishes for its R-panel; other profiles and fastener patterns differ (Berridge's other exposed-fastener profiles are listed at 115 to 155 per square), and wind zones add fasteners. Standing seam panels clip to the deck at spacings set by the maker, so no screw figure is given for them. Not counted: closure strips, eave, rake and valley trim, flashing, underlayment, sealant, hips and valleys, and openings (panels are cut around a skylight or chimney, and the panel count does not change). The metric toggle shows lengths in m or mm and areas in m².

Berridge Metal Roof and Wall Panels, "R" Panel Exposed Fastener Panel System, Sweets (sweets.construction.com): 36 in of coverage, estimate 115 fasteners per square, factory lengths to 40 ft. The same Sweets listings give 115 to 155 per square for Berridge's other exposed-fastener profiles
Western States Metal Roofing, AG Panel product data sheet: 36 in coverage, 3/4 in rib on 9 in centers, recommended minimum roof slope 3/12, lengths 1 ft to 45 ft
Metal Sales Manufacturing, Classic Rib Summary Brochure and Installation Instructions: 36 in coverage R-type panel (buildsite.com document library)
Berridge Metal Roof and Wall Panels, Zee-Lock Panel Standing Seam System, Sweets and the Berridge Zee-Lock data sheet: a 2 in high mechanically seamed panel with 16 in coverage, factory lengths to 40 ft; the Tee-Lock is 18 in coverage
Texas Department of Insurance, windstorm product evaluation reports (RC series) for R, RPN and PBR panels: an eave projection of 2 in past the fascia as the limit in the evaluated installation; fastener type and spacing set by design wind pressure
Metal roofing retailer installation guides (metalroofingsource.com, "installing the ridge cap"): ridge cap in 10 ft 6 in pieces covering 10 ft of ridge with a 6 in lap; about 1 in of panel past the eave with gutters. A trade guide, not a maker's data sheet, so the wrapper or the maker's manual rules
Pitch factor √(1 + (rise ÷ 12)²): the slope length of a roof for each unit of horizontal run (the Pythagorean theorem), as used in the shingles and rafter length calculators

How to calculate metal roofing

Measure the roof length and span. Measure the building length along the eave and the span across the rafters from the outside of the walls, and the overhang at the eaves and the gable ends.
Find the pitch. Measure the rise in inches over 12 in of run, for example 6/12. The slope calculator can turn an angle or percent into x/12.
Count the panels per side. Divide the roof length (building length plus the overhang at each end) by the panel coverage width, 36 in for an R-panel or 16 in for standing seam, and round up.
Work out the panel length. Multiply the run (half the span for a gable) plus the overhang by the pitch factor √(1 + (rise ÷ 12)²), add the hang past the eave, and round up to the inch.
Total the panels and trim. Multiply the panels per side by the number of planes, add any spares, and count ridge cap at 10 ft of ridge per piece. Check screws, closures and trim against the maker's data sheet.

Worked examples

Project	Result
36 × 28 ft building, gable roof, 6/12 pitch, 12 in overhang, 36 in exposed-fastener panels	26 panels (13 a side), each 16' 11" long; 1,320 sq ft of panel, 4 pieces of ridge cap, about 1,466 screws
40 × 30 ft building, gable roof, 4/12 pitch, 12 in overhang, 16 in standing seam panels, 5% spare	68 panels (64 plus a spare; 32 a side), each 17' 0" long; 1,541 sq ft of panel, 5 pieces of ridge cap
20 × 12 ft shed roof, 3/12 pitch, 12 in overhang, 2 in past the eave edge, 36 in panels	8 panels, each 13' 7" long, one plane; 326 sq ft of panel, 3 pieces of high-side trim, about 340 screws

Frequently asked questions

How many metal roof panels do I need?: Divide the roof length by the panel's coverage width, round up, and multiply by the number of roof planes. The example roof is 38 ft long (36 ft plus a 12 in overhang at each end), so 12.67 panels of 36 in coverage is 13 on each side, and 26 in all for a gable roof. A last panel is usually ripped to width, so the count always rounds up.
What is the coverage width of a metal roof panel?: It is what one panel covers after its side lap or seam is overlapped, and it is less than the overall width. R-panel, AG panel and Classic Rib profiles are sold with 36 in of coverage (a sheet of about 37 3/4 in overall); standing seam panels are commonly 16 in, for example Berridge's Zee-Lock, with 12 and 18 in profiles also made. This calculator offers 36 in and 16 in. If your panel differs, divide the roof length by its coverage width yourself.
How long should I order the panels?: Panels run in one piece from the eave to the ridge. The length is the run plus the overhang, times the pitch factor, plus the hang past the eave edge, rounded up to the inch: 16' 10 1/4" for the example, so 16' 11". Makers roll panels to length, commonly up to 40 ft, so one order covers most house roofs. Check with your supplier about set-back at the ridge, and about the cut length for a roof over 40 ft.
How far should metal panels overhang the eave?: Enough for water to drip clear of the fascia instead of running back under the panel. Trade guides give about 1 in over a gutter and 2 to 3 in without one, and Texas wind-product evaluations limit the projection to 2 in past the fascia for the R-panel installations they tested. Follow your maker's manual: this calculator adds the figure you enter to the panel length.
How many screws does a metal roof need?: For exposed-fastener panels the page estimates 115 per square (100 sq ft), the figure Berridge lists for its R-panel; the example roof comes to about 1,466 screws. Other profiles and patterns need more (Berridge lists up to 155 per square for some), high-wind zones add fasteners, and the maker's pattern and spacing for your panel and purlin or deck rule. Buy extra: screws drop. Standing seam panels clip down at the maker's spacing and need no figure here.
How much ridge cap do I need?: Ridge cap is counted along the roof length. A usual piece is 10 ft 6 in long and covers 10 ft of ridge once the 6 in lap is allowed, so the 38 ft ridge of the example takes 4 pieces. A shed roof has no ridge: the same length of high-side trim goes along the top. Closure strips, eave and rake trim and flashing are bought separately and are not counted here.
What roof pitch can metal panels go on?: Exposed-fastener panels are usually listed for 3/12 and steeper (the AG panel data sheet gives 3/12 as the recommended minimum), and standing seam is used on lower slopes: the IRC (R905.10.2) sets 3/12 for lapped seams without sealant, 1/2 in 12 with lap sealant and 1/4 in 12 for standing seam systems. Slope limits, underlayment and fastening depend on the panel and the maker, so use the data sheet or the supplier for yours. The slope calculator turns an angle or a percent grade into x/12.
Does the calculator handle hips, valleys and dormers?: No. It works a plain gable or shed roof, where every panel is the same length. Hips and valleys need panels cut on a diagonal, with each panel a different length, and a dormer or an addition is its own roof. Work those parts separately with the length and span of each, and ask your supplier to lay out the cut panels.
Do I need underlayment and a permit?: Most manufacturers call for underlayment over solid sheathing and many places require a permit for a re-roof. Underlayment, sealants and closures are not counted here. Check the maker's manual and your local code, and use fall protection: metal roofing is slippery.

Handy tools

Slope Calculator: Turn a rise and run, an angle or a percent grade into the x/12 pitch the field above takes.
Feet and Inches Calculator: Add up building sides measured in feet, inches and fractions, and get decimal feet for the length and span.