How many metal roof panels?
Enter the roof size and pitch, get panels, lengths and trim instantly.
Include the gable overhangs in the length. R-panel and PBR usually cover 36 in; standing seam 12–18 in.
How many metal roof panels do I need?
Divide the length along the eave by the panel's coverage width and round up — that is the count for one slope. A 40 ft long house with 36 inch panels: 480 ÷ 36 = 13.3, so 14 panels per side, or 28 for a gable roof.
How long should the panels be?
As long as the slope from the ridge to the eave, plus the overhang. Take half the house width plus the overhang and multiply by the pitch factor. A 30 ft wide house with a 12 inch overhang and a 4/12 pitch: (180 + 12) × 1.054 = 202.4 inches, so order 203 inch (16 ft 11 in) panels. Metal panels are cut to length, so order them to the inch.
How many squares of metal roofing is that?
Multiply the panel length by the eave length and the number of slopes, and divide by 100. The roof above is 16.92 ft × 40 ft × 2 = 1,353 square feet, or 13.5 squares.
What is the coverage width of a metal panel?
The width a panel covers once it overlaps its neighbor — less than its full width. Exposed-fastener panels like R-panel and PBR usually cover 36 inches, and standing seam panels 12 to 18 inches. Use the coverage width from your supplier.
How much trim do I need?
Ridge cap along the ridge, eave trim along each eave and rake (gable) trim up both edges of each slope. For the 40 × 30 ft roof: 40 ft of ridge cap, 80 ft of eave trim and 67.7 ft of rake trim. Add a little for the overlaps where trim pieces join.
How do I turn a roof pitch into an angle or a length factor?
A pitch of x/12 rises x inches for every 12 inches of horizontal run. The slope is longer than the run by the factor √(1 + (x/12)²): 4/12 gives 1.054, 6/12 gives 1.118 and 12/12 gives 1.414. As an angle, 4/12 is 18.4 degrees, 6/12 is 26.6 degrees and 12/12 is 45.0 degrees.
Why does the count go up in whole panels?
Panels are sold and installed whole, so the last panel on each slope is trimmed to fit. The calculator rounds the number of panels up for that reason, and the panel length up to the next inch, so you never order short.
Does this work for hip roofs or valleys?
No. The calculator covers a gable roof (two slopes) or a shed roof (one slope) with rectangular slopes. A hip, a valley or a dormer cuts panels at angles, and the layout needs to be drawn out or priced by the supplier.
How the calculation works
For each slope the calculator does three things. First, the horizontal run: half the house width for a gable roof, or the full width for a shed roof, plus the eave overhang. Second, the slope length: the run times the pitch factor √(1 + (rise/12)²), rounded up to the next inch. Third, the panel count: the length along the eave divided by the panel coverage width, rounded up. The area in squares (100 square feet each) is the panel length times the eave length times the number of slopes. Hips and valleys are not modeled, and neither is a gap at the ridge, so include the gable overhangs in the length you type.
Worked example: a shed roof
A shed roof over a 24 ft long, 14 ft wide building, with a 6/12 pitch, a 6 inch overhang and panels that cover 16 inches. The run is 14 × 12 + 6 = 174 inches. The pitch factor for 6/12 is 1.118, so the slope is 174 × 1.118 = 194.54 inches, rounded up to 195 inches (16 ft 3 in) per panel.
Along the eave, 288 ÷ 16 = 18, so 18 panels. Total panel length is 18 × 16 ft 3 in = 292.5 linear feet, and the roof covers 390 square feet, or 3.9 squares. Eave trim is 24 ft and rake trim 32.5 ft. A gable roof of the same house would need two slopes of half the width each, and a ridge cap of 24 ft.
Common mistakes
Using the full panel width instead of the coverage width: a panel covers less than its full width once it overlaps its neighbor, and a standing seam panel covers less again. The count must use the coverage your supplier lists. A second slip is measuring the roof in plan view, which leaves out the pitch factor; on a 12/12 roof the slope is 41% longer than the run. A third is forgetting that the eave length should include the gable overhangs, which can add a panel on each slope. For comparison, the 40 ft by 30 ft gable roof in the questions above needs 28 panels 16 ft 11 in long.
Sources: pitch factor √(1 + (rise/12)²) from the geometry of a right triangle; panel coverage widths are the values you enter, so use your supplier's data sheet. Related: roof pitch calculator, roofing squares calculator, rafter length calculator.