Metal Roofing Calculator
How many metal roof panels a gable or shed roof takes and how long to cut them, from the building, the pitch, the overhangs and the panel’s coverage width.
Result
Enter panel coverage width to see the result.
https://calcgallery.com/roofing/metal-roofing-calculator/
Results are estimates for planning only. Actual needs vary with site conditions, products and workmanship. Always confirm quantities with your supplier and follow local building codes and manufacturer instructions. Read the full disclaimer
How to use the Metal Roofing Calculator
- Choose gable or shed, and enter the building's length along the eave and its width from wall to wall.
- Enter the pitch as a rise in 12 or in degrees, the eave overhang measured level, and the overhang at each gable end.
- Enter the panel's coverage width from the manufacturer, and any extra length its installation guide asks for past the eave.
The panel count
slope factor = √(1 + (rise ÷ 12)²)panel length = (width + 2 × eave overhang) ÷ slopes × slope factor + extrapanels a slope = (length + 2 × gable overhang) ÷ coverage width, rounded upA gable roof has two slopes and a shed roof one. The panels run from the eave to the ridge in one piece, so their length comes from the slope and the number from the building’s length. The slope factor is the same one the roof area and roof pitch pages use. On a shed roof the eave overhang is counted at the high wall as well as the low one; if only the low side overhangs, enter half of it and the length comes out right.
Trim
The ridge cap runs the length of the roof including the gable overhangs. The rake trim runs up both edges of every slope, and the eave trim along the bottom of each. These are lengths; how many pieces they make depends on the trim’s stock length and the overlap its maker specifies.
With your numbers
- Panel length = (width + 2 × eave overhang) ÷ slopes × √(1 + (rise ÷ 12)²)
- Panels per slope = (length + 2 × gable overhang) ÷ coverage width, rounded up
Quick reference
Panels round up to whole panels; trim and fasteners are extra.
| Job | Panels to order |
|---|---|
| 40 × 28 ft gable, 6 in 12, 36 in panels | 28 |
| 40 × 28 ft gable, 16 in panels | 64 |
| 40 × 28 ft gable, 4 in 12 | 28 |
| 30 × 24 ft gable, 12 in 12 | 22 |
| Shed, 20 × 12 ft, 3 in 12 | 7 |
| 12 × 8.5 m gable, 0.9 m panels | 28 |
Common questions about the Metal Roofing Calculator
- How many metal roofing panels do I need?
- Twenty-eight panels about 16.77 feet long for a 40 by 28 foot gable roof at 6 in 12, with a 12-inch overhang at the eaves and gables and panels that cover 36 inches. Each slope is 40 feet plus two 12-inch overhangs, 42 feet, and 42 ÷ 3 feet = 14 panels. Two slopes make 28.
- How do I work out the length of a metal roof panel?
- Take the level distance from the ridge to the edge of the eave, which is half the building width plus the overhang on a gable roof, and multiply by the slope factor for the pitch. On a 28-foot-wide house with a 12-inch overhang at 6 in 12, that is 15 feet × 1.118, about 16.77 feet. Add whatever your panel maker asks for beyond the eave.
- Why use the coverage width and not the panel width?
- Because panels overlap. A panel sold as 38 or 39 inches wide may cover 36 inches once its rib laps the next one, and the net figure is what fills the roof. The manufacturer publishes it; this page asks for it rather than assuming one.
- Does the page work for hip roofs?
- No. On a hip roof every panel near a hip is cut on the diagonal to a different length, so a count by width does not describe the order. The roof area page gives the area of a hip roof at the same pitch, which is where a hip roof order starts.
- What about screws, closures and underlayment?
- They come from the panel maker’s installation guide and fastening schedule, which differ by profile and by wind exposure. The page gives the panel count and the trim lengths, and leaves the rest to the guide and your local code.