Metal Roofing Calculator
Find how many metal roof panels to buy and how long to order them for each face of a gable or shed roof. Enter the eave length with the run and pitch, or the slope length, choose a panel profile, and see the panels for each face, the total panel length, and the roof area in squares. For asphalt shingles, use the Roofing Calculator.
Measure the eave length along the bottom edge of each face, including any overhang at the ends. Measure the run level from the eave edge to the ridge, such as half the width of a gable roof plus the overhang.
Add a section for each roof face, or set Quantity to 2 for the two faces of a gable roof.
- Choose US or Metric. You can still change the unit of any single field.
- Choose how you measured the roof. With Run and pitch, enter the run measured level from the eave edge to the ridge, such as half the building width plus the overhang, and the pitch as x/12 or in degrees. With Slope length, enter the length measured on the roof from the eave edge to the ridge.
- Enter the Eave length of each face along its bottom edge, including the overhang at the gable ends. For the two faces of a gable roof, enter one face and set Quantity to 2. Use Add section for faces of other sizes, such as a porch.
- Choose the Panel profile. For another panel, choose Custom width and enter the coverage width from its data sheet.
- Check the Panel overhang, how far the panels run past the eave edge. It starts at 2 in (50 mm).
- Optionally, enter a price per foot or meter of panel, or per area, to estimate the cost.
Don't subtract skylights or chimneys: the panels still run from the eave
to the ridge and are cut around them. Length fields accept whole numbers,
decimals, fractions, and mixed numbers, such as 42,
16.5, 3/4, or 21 1/3. Choose
ft + in as the unit to enter a length such as 12 ft 6 in
in two fields. The pitch takes whole numbers and decimals, such as
6 or 22.5.
How to calculate metal roofing panels
The panels run straight from the eave to the ridge, side by side along the eave. For each face, the calculator divides the eave length by the coverage width of the panel and rounds up, then adds the overhang to the length of the face:
Panels per face = eave length ÷ coverage width, rounded up
Slope length = run × √(1 + (rise ÷ 12)²)
Panel length = slope length + panel overhang
Total panel length = panels × panel length, for every face
For a pitch in degrees, the factor is 1 ÷ cos(angle). A 6/12 roof has a factor of about 1.118, so a 16 ft run is about 17.89 ft on the slope. If you measured the slope length on the roof, the calculator uses it as it is. This is the same as the rafter length without the overhang, and the panels run all the way to the ridge: any gap left at the ridge for a vent is cut on site.
Metal roofing manufacturer Central States estimates panels the same way in its guide to calculating roofing material: a face 36 ft along the eave takes 12 panels of 36 in coverage. A face that is shorter than one panel still takes one panel.
Roof area
Roof area = eave length × slope length, for every face
The roof area leaves out the overhang and doesn't depend on the panel. It is shown in ft², squares (100 ft²), and m², so you can compare metal with shingles or price the roof by area. Metal panels are sold by length, so the panels and total length are what you order.
Panel coverage widths
The coverage width is how much roof one panel covers after it overlaps the next one at the side. It is narrower than the full width of the sheet, so use the coverage width from the panel's data sheet, not the sheet width. The profiles in the calculator use these widths:
US panels
| Profile | Coverage |
|---|---|
| 36 in ribbed panel | 36 in |
| 5V crimp | 24 in |
| 2 1/2 in corrugated | 21 1/3 in |
| 16 in standing seam | 16 in |
Source: Metal Sales PBR-Panel and 5V-Crimp, MBCI 5V Crimp, Central States Panel-Loc Plus and Central Snap, and Fabral Grandrib 3, 2 1/2" Corrugated, and Horizon 16.
Metric panels
| Profile | Coverage |
|---|---|
| 762 mm corrugated | 762 mm |
| 700 mm concealed-fix | 700 mm |
| 1000 mm box profile | 1000 mm |
| 990 mm corrugated | 990 mm |
Source: Lysaght Custom Orb, Trimdek, Klip-Lok 700, and Spandek, and Cladco 32/1000 Box Profile and 13/3 Corrugated.
The 36 in ribbed panel covers both R-panels and PBR panels with ribs 12 in apart and ag panels with smaller ribs 9 in apart. The 2 1/2 in corrugated width is for a roof, where Fabral laps two corrugations at the side: the same sheet covers 24 in on a wall, and Gibraltar Building Products lists 21 1/2 in for its roof panel, so the narrower width is used. Standing seam panels come in other widths too, such as 18 in and 24 in; choose Custom width for those.
In Australia and New Zealand, corrugated and trapezoidal sheets often cover 762 mm, and clip-fixed and some trapezoidal sheets 700 mm, as in Lysaght's installation manual. UK box profile and corrugated sheets, such as Cladco's, cover about 1000 mm and 990 mm. The Metric profile starts at 1000 mm box profile in the UK and Ireland and at 762 mm corrugated elsewhere. The widths are typical values, not a match for every product, so check the coverage or cover width of the panel you buy.
Panel overhang at the eave
The panels usually run a little past the eave edge so that water drips clear of the fascia or into the gutter. The overhang is measured along the panel. Fabral's details allow 1 to 2 in at the eave for a drip edge, and Central States suggests about 1 in with gutters and warns that 6 in or more may not hold snow. The US default is 2 in, the top of Fabral's range, because a panel cut too short can't be extended.
The Metric default is 50 mm, close to 2 in. New Zealand's Metal Roofing Manufacturers code of practice recommends at least 50 mm where the sheet ends overhang a gutter, and at least 70 mm where they don't. Lysaght gives no number and says to overhang the sheets into the gutter. Set the overhang to suit your gutters and the panel's installation guide.
Panel lengths and minimum pitch
Panels are made in lengths up to a limit that depends on the product and on shipping, such as about 45 ft for Metal Sales 5V-Crimp, 40 ft for Fabral 2½" Corrugated, 7 or 9 m for Cladco's box profile depending on the thickness, and the transport limits for Lysaght. Most house roofs are shorter than that, so the calculator doesn't split long panels. For a longer face, check your supplier's limit and lap the panels at the ends; Central States notes that most end laps take 6 in.
The calculator doesn't check the pitch against the panel. The lowest pitch varies by product: 3/12 for Metal Sales 5V-Crimp, 1/12 for Metal Sales PBR-Panel, 2 1/2/12 for Fabral 2½" Corrugated, and 5° for Lysaght Custom Orb. Check the data sheet of the panel you choose.
Waste and cost
There is no waste allowance. Each face is rounded up to whole panels, and the panels are cut to the length of each face, so there are no offcuts from stock lengths. Central States notes that many buyers order one extra full-length panel for each face with valleys, dormers, or other obstructions, to allow for cutting mistakes. Add one to the count for those faces.
Metal panels are usually priced by the linear foot or meter, so the price starts per ft (per m in Metric) and uses the total panel length. A New Zealand supplier, for example, adds up sheets the same way: seven sheets of 3.9 m make 27.3 m. Choose per ft², per square, or per m² for a price by roof area, such as an installed price or a price to compare with shingles. The cost covers the panels you price: enter a price that includes installation to include it.
Examples
A gable roof with 36 in panels
Each face of the roof is 42 ft along the eave with a 16 ft run at 6/12. The slope length is 16 × √1.25 = 17.89 ft, so with a 2 in overhang each panel is 18 ft 11/16 in. Each face takes 504 ÷ 36 = 14 panels, so the two faces take 28 panels, 505.55 ft of panel. The roof area is 42 × 16 × √1.25 × 2 = 1,502.64 ft², or 15.03 squares. At $3.00 per foot, the panels cost about $1,516.64.
Measured on the slope
A shed roof 20 ft along the eave and 12 ft 6 in on the slope, with 5V crimp panels of 24 in coverage, takes 240 ÷ 24 = 10 panels of 12 ft 8 in, or 126.67 ft. The roof area is 250 ft², or 2.50 squares.
A Metric roof
Each face is 10 m along the eave with a 4 m run at 22.5°. The slope length is 4 ÷ cos 22.5° = 4.33 m, so with a 50 mm overhang each sheet is 4,379.6 mm. With 762 mm corrugated sheets, each face takes 10 ÷ 0.762 = 13.12, rounded up to 14, so the roof takes 28 sheets, 122.63 m. With 1000 mm box profile, it takes 20 sheets.
FAQ
About 14 panels for each face 42 ft along the eave, with 36 in coverage: 42 × 12 = 504 in, and 504 ÷ 36 = 14. Divide the eave length of each face by the coverage width of the panel and round up.
As long as the face from the eave edge to the ridge, plus the overhang. A 16 ft run at 6/12 is about 17.89 ft on the slope, so with a 2 in overhang the panels are 18 ft 11/16 in.
Often 1 to 2 in in the US, such as 1 in with gutters. New Zealand's code of practice recommends at least 50 mm into a gutter and 70 mm without one. Check the panel's installation guide.
Enter each face as its eave length by its longest slope length. You get the panels at full length to cut on site. The roof area comes out high, so use the Roofing Calculator for the area.
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