Metal Roofing Calculator

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 length

Worked 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

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 full length of the slope plus 1 to 2 inches of overhang at the eave. Most suppliers cut to the inch, so one panel per row avoids an end lap. If the slope is longer than the supplier can deliver, plan an end lap of at least 6 inches over a purlin.

Screws, closures and trim

Exposed-fastener panels use screws with a bonded sealing washer, driven through the flat of the panel into purlins or solid decking on a grid of roughly 24 inches. That works out to about 80 screws per square. Standing seam panels are held by clips under the seam, typically one every 12 to 24 inches along each seam.

Foam closure strips fill the panel profile at the eave and under the ridge cap to keep out wind, rain and insects. Ridge cap comes in 10 foot lengths and covers the full eave length. Add rake trim for the gable ends, eave trim or drip edge, and sidewall or endwall flashing where the roof meets a wall. Local code and the panel manufacturer's installation guide govern underlayment and fastener spacing.

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

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)