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Metal Roofing Panel Calculator

Works out metal roofing panels from the eaves length and the slope, with screws and ridge flashing. Uses cover width rather than sheet width, which is where most estimates go wrong.

slopes
mm

The covering width after the side lap, not the overall sheet width. A 1090 mm sheet typically covers 1000 mm.

m

Panels longer than this need an end lap. Most suppliers go to 6 m; longer is possible but awkward to handle.

mm
%

Metal panels are cut to length, so waste is low on a simple roof. Allow more where there are hips or valleys.

Optional. Enter what your supplier quotes and pick the basis they quote it on.

Panels needed
— panels

Share sends a link that reopens these numbers. Copy details pastes the full breakdown as a list.

Panels across each slope — panels
Length of each panel —
Rows up the slope — rows
Area covered —
Fixing screws — screws
Ridge flashing —
Panel cost —
Ordering them —

The formula

panels per slope = ceiling(eaves length ÷ cover width) panels = panels per slope × rows up the slope × slopes × (1 + waste)

Cover width is the figure that matters and it is not the sheet width — the side lap overlaps the neighbouring panel and covers nothing. Using the overall width under-orders by roughly one panel in twelve.

What to watch out for

Three things decide the order:

  • Cover width, not sheet width. A sheet 1090 mm wide covers 1000 mm once lapped. Order on the covering figure.
  • Single-length panels if possible. A panel running eave to ridge in one piece has no end lap, and end laps are where metal roofs leak.
  • Screws go in the flat, not the rib, on most exposed-fastener profiles — with the washer compressed just enough to seal and no more. Over-tightening dimples the sheet and breaks the seal, which is the second most common leak after laps.

Metal expands and contracts noticeably with temperature. Long panels need fixings that allow movement, or the holes elongate and start to leak after a few seasons.

Frequently Asked Questions

How many metal roofing panels do I need?

Divide the eaves length by the panel cover width and round up, then multiply by the number of slopes. A 10 m eave with 1000 mm cover panels needs 10 panels per slope, so 20 for a simple gable.

What is the difference between cover width and sheet width?

Cover width is what the panel actually covers once the side lap overlaps its neighbour. A 1090 mm sheet typically covers 1000 mm, so ordering on sheet width leaves you about 9% short.

How many screws per square metre for metal roofing?

About 8 for a standard exposed-fastener profile, so a 100 m² roof needs roughly 880 including spares. Eaves, ridge and laps are fixed more densely than the field.

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