How many metal roofing panels do I need?
Panels across = the width of the roof plane in inches (feet x 12) divided by the coverage width of one panel, rounded up. [1] Rows up the slope = 1 if one panel is long enough, otherwise each further panel adds its length minus the end lap. Panels = across x rows, for each plane.
To measure the roof, find the width along the eave and the length up the slope of each plane. For a roof with several different planes, calculate each on its own and add the panels. The roofing calculator on this site finds the area of a simple roof from its footprint and pitch.
We found no source for an extra on metal roofing, so Extra to order starts at 0. Ask your supplier how many spare panels to add.
Worked example
A roof plane 30 ft wide and 15 ft up the slope. A panel covers 36 in, so 30 ft x 12 = 360 in, and 360 / 36 = 10 panels across. The panel is 16 ft long, which reaches past the 15 ft slope, so it is 1 row. 10 x 1 = 10 panels. The roof area is 30 x 15 = 450 square feet.
Coverage width: use it, not the overall width
Metal Sales lists a panel coverage of 36 inches for its Verti-Rib panel. [2] Gibraltar says that its corrugated panel, laid with an overlap of 2 corrugations, gives each panel 21-1/2 inches of width coverage. [4] Those two figures are examples: the coverage width of your own panel is on its data sheet.
Why the coverage width
The coverage width is the width one panel covers once it is laid, with the side overlap taken out. Counting with the overall width would give too few panels.
End laps and side overlap
Gibraltar says the overlap on the sides of a panel depends on the profile, and is in each panel's detail manual, and that the overlap of panels down the pitch of the roof must be 12 inches. [3] Enter the end lap for your panel under End lap.
A slope longer than one panel takes more rows. Each extra row adds the panel length minus the end lap. For 16 ft panels with a 12 in end lap, a 30 ft slope needs 2 rows, because 16 + 15 = 31 ft.
| Slope length (ft) | Rows | Panels on a 30 ft wide plane |
|---|---|---|
| 10 | 1 | 10 |
| 15 | 1 | 10 |
| 20 | 2 | 20 |
| 30 | 2 | 20 |
| 40 | 3 | 30 |
How many sheets of metal roofing do I need?
Read Panels to order above. For the example it is 10 panels of 36 in coverage, 16 ft long, for one plane 30 ft wide and 15 ft up the slope.
What is the lowest slope for metal roofing?
Metal Sales lists a minimum roof slope of 3:12 for its Verti-Rib panel. [2] Gibraltar says the lowest recommended pitch for its corrugated roofing panels is 3:12. [4] Other panels and your local rules may differ: check your own panel and ask your building authority.
How do I find the roof area?
Area = the width of the plane times its length up the slope, for each plane. The example is 30 x 15 = 450 square feet. If you know the flat size of the building and the pitch instead, the roofing calculator and the roof pitch calculator give the roof area and the slope length.
Purlins and battens
We found no source we can cite for the spacing of purlins or battens. It comes from your panel maker's installation guide, so ask them.
How many screws per metal roofing sheet?
We found no source we can cite for the number of screws, so this calculator does not count them. Your panel maker's installation guide gives the fastener pattern.
How much does metal roofing cost?
We state no price. Ask local suppliers for the price of one panel, then enter it under Price (optional) above to see the total for the panels to order. The site does not store the prices you type.
Common mistakes and limits
- Counting with the full panel width. Use the coverage width. Metal Sales lists 36 inches of coverage for its Verti-Rib panel. [2]
- Forgetting the end lap. Gibraltar says the overlap of panels down the pitch of the roof must be 12 inches. [3]
- Counting the planes once. Enter 2 under Identical roof planes for a gable roof with two equal sides.
- What this tool does not cover: trim, flashing, ridge caps, underlayment, fasteners and the roof structure.
Frequently asked questions
Do I use the full width or the coverage width of a panel?
Use the coverage width, which is what one panel covers once it is laid. Metal Sales lists a coverage of 36 inches for its Verti-Rib panel, and Gibraltar says its corrugated panel laid with an overlap of 2 corrugations gives each panel 21-1/2 inches of width coverage. [2][4]
How much overlap do metal roofing panels need?
Gibraltar says the overlap on the sides depends on the profile, and is in each panel's detail manual, and that the overlap of panels down the pitch of the roof must be 12 inches. Use the figures for your own panel. [3]
What is the lowest roof slope for metal panels?
Metal Sales lists a minimum roof slope of 3:12 for its Verti-Rib panel, and Gibraltar says the lowest recommended pitch for its corrugated panels is 3:12. Other panels and your local rules may differ. [2][4]
How long can a metal roofing panel be?
Metal Sales lists a panel length from 5 feet to a recommended maximum of 45 feet for its Verti-Rib panel. Your panel's data sheet gives its own limits. [2]
How much does a sheet of metal roofing cover?
Its coverage width times its length, less the end lap where one panel is laid above another. A 36 in coverage panel 16 ft long covers 3 ft x 16 ft, which is 48 square feet, before any end lap.
Sources and references
- National Institute of Standards and Technology (NIST). NIST Guide to the SI, Appendix B.8: Factors for Units Listed Alphabetically (SP 811, accessed November 2026). Used for: the inch and foot relationship (12 inches in a foot).
- Metal Sales Manufacturing Corporation. Verti-Rib Product Data (accessed November 2026). Used for: one panel's coverage width, panel length limits and lowest roof slope.
- Gibraltar Building Products. How much overlap is needed on metal roofing panels? (accessed November 2026). Used for: that the side overlap depends on the profile, and the overlap down the roof.
- Gibraltar Building Products. Minimum or recommended slope for a corrugated galvanized steel roof panel (accessed November 2026). Used for: the lowest recommended pitch and the coverage width of a corrugated panel.
How we use sources: methodology.
Estimates only. Confirm quantities with your supplier. See the disclaimer. Found a wrong result? Report an error.