How many metal roofing panels do I need?

Divide the eave length of each roof plane by the panel’s coverage width — not its overall width — and round up. A 40 ft eave with 36 in coverage panels is 480 ÷ 36 = 13.3, so 14 panels a side, 28 for a simple gable. The last panel on each side is ripped down to fit.

What length should I order metal roof panels?

Measure the slope from the eave edge to the ridge along the roof, then add the overhang you want past the eave. A 14 ft slope with a 2 in overhang is a 14 ft 2 in panel. Most suppliers cut panels to length, so order the exact figure rather than rounding up to a stock size.

Why use coverage width instead of panel width?

Panels overlap at the side lap, so a sheet that is 38 or 39 in wide might only cover 36 in. The coverage figure is on the manufacturer’s sheet. Divide by the overall width and you come up a panel or two short on every side.

How many screws do I need for a metal roof?

Take the screws-per-panel figure from the manufacturer’s fastening pattern for your panel length and purlin spacing, and multiply by the number of panels. The pattern depends on the product and the job, so the calculator only does the multiplication with the figure you type.

Metal roofing calculator

Longueur du toit (par versant)

Le long de l’avant-toit, débords de rive compris. En pieds, ou comme 40' 6".

Longueur en pente jusqu’au faîte

Mesurée en suivant la pente du toit, pas en plan.

Largeur utile du panneau

La couverture nette selon la fiche du produit, après le chevauchement latéral.

Débord à l’avant-toit

Au-delà du bord de l’avant-toit, ajouté à chaque panneau.

Versants

versants

Vis par panneau

vis

— panneaux à commander

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The count divides your eave by the coverage you type and adds your overhang to the slope. It says nothing about purlin spacing, fastening pattern, wind or snow load, or whether the panel suits the pitch — those come from the manufacturer and your code. Hips, valleys and dormers waste more than a simple gable.

Enter each roof plane's eave length and slope length, the panel's coverage width and the overhang you want. The calculator rounds the panels up per plane, gives the length to cut them to as a tape reading, totals them for all the planes and, with your screws-per-panel figure, counts the fasteners.

Exemple détaillé

Imperial. A gable roof, two planes each 40 ft along the eave and 14 ft eave to ridge, in 36 in coverage panels with a 2 in overhang. Per plane: 480 ÷ 36 = 13.3 → 14 panels, the last ripped to 12 in of coverage. Both planes: 28 panels at 14′ 2″, 396.7 linear feet of panel over 1,120 ft² (11.2 squares) of roof. At the pattern's own figure — say 30 screws a panel — that is 28 × 30 = 840 screws.

Metric. Two planes 12 m along the eave and 4.2 m eave to ridge, 914 mm coverage, 50 mm overhang. Per plane: 12,000 ÷ 914 = 13.1 → 14 panels. Both planes: 28 panels at 4,250 mm, 119 m of panel over 100.8 m² of roof.

Sur le chantier

Order the exact length. Most panel is cut to the inch or the millimetre at the plant, and a panel 3 in too long is a panel you trim on the roof with snips. Measure each plane — an old roof can differ by an inch or more from one end to the other — and order to the longest.

Start square, not at the corner. Run the first panel off a line square to the eave, not off the rake. If the rake is out, the last panel goes on at an angle and the ripped piece at the far end is tapered — measure the eave at both the top and bottom before you rip it.

Screws come in bags. Round the screw count up to whole bags and add a handful for the trim and the ones that fall off the roof — trim, ridge cap and flashings all take their own.

What went wrong?

Quick referencefor metal panels

Panels per plane: eave length ÷ coverage width, rounded up
Panel length: slope length + eave overhang (+ any ridge allowance on the spec)
Panels per 10 ft of eave: 36 in coverage: 3.33 · 24 in: 5 · 16 in: 7.5
Coverage in metric: 36 in = 914 mm · 24 in = 610 mm · 16 in = 406 mm
A square: 100 ft² of roof = 9.29 m²

La formule

panels = ⌈eave ÷ coverage⌉ × planes · length = slope + overhang · screws = panels × screws per panel

Each plane is counted separately and rounded up on its own, because a ripped panel on one side cannot finish the other. The slope length is measured on the roof; if you only have the run and the pitch, work it out on the rafter length calculator first.

Questions

How many metal roofing panels do I need?: Divide the eave length of each roof plane by the panel’s coverage width — not its overall width — and round up. A 40 ft eave with 36 in coverage panels is 480 ÷ 36 = 13.3, so 14 panels a side, 28 for a simple gable. The last panel on each side is ripped down to fit.
What length should I order metal roof panels?: Measure the slope from the eave edge to the ridge along the roof, then add the overhang you want past the eave. A 14 ft slope with a 2 in overhang is a 14 ft 2 in panel. Most suppliers cut panels to length, so order the exact figure rather than rounding up to a stock size.
Why use coverage width instead of panel width?: Panels overlap at the side lap, so a sheet that is 38 or 39 in wide might only cover 36 in. The coverage figure is on the manufacturer’s sheet. Divide by the overall width and you come up a panel or two short on every side.
How many screws do I need for a metal roof?: Take the screws-per-panel figure from the manufacturer’s fastening pattern for your panel length and purlin spacing, and multiply by the number of panels. The pattern depends on the product and the job, so the calculator only does the multiplication with the figure you type.

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