What is the difference between coverage width and overall width?

Overall width is the physical edge-to-edge dimension of the sheet. Coverage width is what it actually covers once it laps the panel beside it — commonly 36 inches of coverage on a panel that measures around 38 inches overall. Calculating with the overall width overstates coverage by roughly five percent, which is a short order on every job.

How many screws does a panel take?

It depends on purlin or girt spacing and whether the panel is fastened through the flat or at the rib. Forty to sixty per 3 ft × 20 ft panel is a common range. Count the fastening rows your framing spacing implies, multiply by the fasteners across the panel width, and use that rather than a rule of thumb if the spacing is unusual.

Should I order panels to full length or lap them?

A single panel running eave to ridge has no endlap, which is both faster and far less prone to leaking. It is the reason suppliers cut to order. Lapping is a shipping and handling compromise for very long slopes, and it needs sealant tape and a longer overlap, so treat it as a last resort rather than a default.

What waste allowance is right?

Ten percent covers cuts around openings and the occasional damaged sheet. Increase it for a roof with many penetrations, valleys or dormers, and for any building where panels run diagonally. Trim and closures are separate from this figure, not covered by it.

Does this include trim and closures?

No — panels and screws only. Ridge cap, eave and rake trim, corner trim, base trim, inside and outside closures, sealant tape and pipe boots are all separate line items, and together they are a meaningful share of an envelope quote. Price them from your supplier's list.

Metal Roofing & Siding Panel Calculator

Count the metal roofing or siding panels a building needs from coverage width and panel length, with screws and waste — priced at your supplier's rate.

By StatesideCalc EditorialLast verified July 27, 2026

Area to cover

Roof planes or wall elevations. Run roof and walls separately.

sq ft

Panel coverage width

Net coverage after the sidelap — usually 36 in on rib panel.

Panel length

Price per panel

Each panel covers 60 sq ft. Use the coverage width from the spec sheet, not the overall width — the difference is the sidelap, and using overall width shorts every order.

What this calculator does

Metal panel is sold by the sheet, cut to the length you order, and the quantity turns on one number people routinely get wrong: coverage width. Get that right and the count is simple division. Get it wrong and you are five percent short on every job — which on a 40 × 60 building is several sheets and a delay.

Coverage width, not overall width

A standard rib panel measures around 38 inches edge to edge and covers 36 inches once it laps the sheet beside it. The two-inch difference is the sidelap, and it does no covering.

coverage per panel = (36 ÷ 12) × 20 ft = 60 sq ft

Divide the area by that, add waste, round up to whole sheets. The spec sheet always prints the coverage figure — use it, and be sceptical of any calculator that asks only for “panel width” without saying which one it means.

Run roof and walls separately

They are different areas with different waste profiles, and often different panel profiles or gauges. Two runs of the calculator is the right approach.

For the roof, remember the sloped area is larger than the footprint. If you have not worked that out yet, the roofing calculator applies the pitch multiplier, and how to measure a roof for shingles explains the geometry — it is the same trigonometry whether the covering is asphalt or steel. For a post-frame building, the post-frame calculator reports the sloped roof area and the wall area directly.

Panel length: order long if you can

A panel that runs unbroken from eave to ridge has no endlap. Endlaps are the most common leak location on a metal roof, they need sealant tape and a generous overlap, and they add labour. Suppliers cut to order precisely so you can avoid them.

The practical limits are shipping and handling, not manufacturing — a 40-foot panel is awkward on a truck and worse on a windy roof with two people. Past roughly 30 feet, weigh the endlap against the handling honestly.

Screws are not a rounding error

At forty to sixty fasteners per panel, a modest building runs into the thousands. They are also the part of the envelope that fails first: the washers degrade under UV long before the panel does, and a re-screw is a routine mid-life job on an exposed-fastener roof.

Two things worth deciding at order time. Buy fasteners rated for the panel coating — mismatched metals corrode at the contact point. And if long service with minimal upkeep matters more than upfront cost, that is the argument for a standing-seam concealed-fastener system instead, which this calculator’s exposed-fastener assumptions do not describe.

What is not counted

Panels and screws. Everything else on the envelope is separate:

Ridge cap, eave, rake, corner and base trim, sold by the length
Inside and outside closures at the ribs
Sealant tape, pipe boots, and any curb flashing
Insulation and vapour barrier — priced against area in the building cost calculator

On a typical building those add up to a real fraction of the envelope, so a panel-only figure is a starting point rather than a quote.

For installation standards, fastener practice and panel profiles, the Metal Building Manufacturers Association and the Metal Construction Association publish the references the trade works from.

How this is calculated

coverage per panel = (coverage width in ÷ 12) × panel length ft panels = ceiling( area ÷ coverage per panel × (1 + waste) ) screws = panels × screws per panel Use the NET coverage width from the spec sheet, not the overall width — the difference is the sidelap.

Frequently asked questions

What is the difference between coverage width and overall width?: Overall width is the physical edge-to-edge dimension of the sheet. Coverage width is what it actually covers once it laps the panel beside it — commonly 36 inches of coverage on a panel that measures around 38 inches overall. Calculating with the overall width overstates coverage by roughly five percent, which is a short order on every job.
How many screws does a panel take?: It depends on purlin or girt spacing and whether the panel is fastened through the flat or at the rib. Forty to sixty per 3 ft × 20 ft panel is a common range. Count the fastening rows your framing spacing implies, multiply by the fasteners across the panel width, and use that rather than a rule of thumb if the spacing is unusual.
Should I order panels to full length or lap them?: A single panel running eave to ridge has no endlap, which is both faster and far less prone to leaking. It is the reason suppliers cut to order. Lapping is a shipping and handling compromise for very long slopes, and it needs sealant tape and a longer overlap, so treat it as a last resort rather than a default.
What waste allowance is right?: Ten percent covers cuts around openings and the occasional damaged sheet. Increase it for a roof with many penetrations, valleys or dormers, and for any building where panels run diagonally. Trim and closures are separate from this figure, not covered by it.
Does this include trim and closures?: No — panels and screws only. Ridge cap, eave and rake trim, corner trim, base trim, inside and outside closures, sealant tape and pipe boots are all separate line items, and together they are a meaningful share of an envelope quote. Price them from your supplier's list.