Corrugated Metal Panel Side Lap Overlap Calculator

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Market

Imperial · sales tax

Total Roof Width

The total width of roof to be covered, measured across the panel runs.

Across the runs, which is the direction in which side laps accumulate. Each lap consumes part of a sheet's width, so the width a panel actually COVERS is less than the width it is made — and the sheet count is not the roof width divided by the sheet width. On a wide roof that difference is several sheets.

Panel Width (Out-to-Out)

The panel's full out-to-out width, before accounting for overlap.

This is the panel's overall coil/cut width — not the net width it actually adds once overlapped with the next panel.

Side Lap Width

How much of each panel's width overlaps the adjacent panel along its side lap.

Set by the profile — normally a whole number of corrugations, because a lap that lands mid-corrugation does not seat — and by exposure. A shallow pitch or a windy site needs a wider lap and often a sealed one, since wind drives water uphill along a lap. Trimming the lap to save sheets is the standard cause of the capillary leaks that appear in a line down the roof.

Panels needed

20 panels

High confidence

Net coverage width per panel: 3.33 ft

Then change the inputs to see how far the answer moves.

Show calculation logic

How this was calculated

Formula source(s)

Net coverage width per panel = panel width − side lap width; panels needed = ceil(total roof width ÷ net coverage width per panel)

Inputs used

Total Roof Width: 66 ft
Panel Width (Out-to-Out): 3.5 ft
Side Lap Width: 2 in

Intermediate steps

Net coverage width per panel: 3.33 ft

Final result20 panels

What this calculation does not cover

How many panels is settled here; which panel is not. Gauge and profile depth are chosen against the purlin spacing and the wind and snow the sheet has to carry between supports, so the same count in a thinner or shallower profile deflects between purlins, holds water at the laps and oil-cans in the flats.

Estimated cost — your price

Price per panel ($)

This site holds no price list for this material — local prices vary too much to publish honestly. Enter your supplier's price and the result is costed with it.

Schematic, drawn to the proportions you entered — not to scale on screen.

Computed in your browser — nothing you enter is uploaded. Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.

Sources checked 2026-09-06 · in the site-wide review of 2026-09-06 · v1.0.1

Regulatory standards & verification citations1

Net coverage width per panel = panel width − side lap width; panels needed = ceil(total roof width ÷ net coverage width per panel)

Cite this page

Your workspace

Most jobs need more than one number. Add the calculators you need next and they open right here, underneath this one — your figures stay on screen and nothing is lost to a page change.

Tools and safety for this job

To fix roof sheeting and soffit panels. Generic types, no brands, no prices.

Protection this work requires

Most fatal falls on small jobs are from under three metres: use a tower or a ladder tied at the top, and never work off the top two rungs.
Knives cause more site injuries than any power tool: cut away from your body, change blades often, and wear cut-resistant gloves to EN 388 level C for repeated cutting.

Fix roof sheeting and soffit panels: Roof work is the commonest cause of serious fall injury on domestic sites, and profiled sheeting adds a danger of its own: older fibre-cement and plastic sheets, and the rooflights set among them, can give way under a person's weight without warning. Edge protection or a properly erected tower is the equipment that matters most here, and a roof that is fragile, steep, high or wet is a job for a roofer with the right access and staging, not a longer ladder.

Show the 6 tools this job needs

Essential

Chalk line
Extension ladder
Impact driver
Metal snips
Tape measure
Tower scaffold or trestles

Also needed as materials: chalk refill, impact driver bits.

what each roofing tool is for, and the spec that decides which to buy where one does.

Now that you have the number

These guides cover the work this quantity is for — the first ones run this calculator inside the section that raises the question.

Cladding a Portal Frame: Built-Up or Composite Paneluses this calculator

Twin skin built up on site against factory composite panel, and the spacer bar that quietly caps the U-value whatever thickness of quilt you buy.

Fitting a Radiant Barrier Under a Metal Roofuses this calculator

Foil lands in the gap between the steel gang and the sheeters, and the roll count, the lap allowance and the condensation risk are all settled before it does.

Installing a Standing Seam Metal Roof

How to calculate corrugated metal panel side lap overlap in 4 steps

Total Roof WidthThe total width of roof to be covered, measured across the panel runs.

Panel Width (Out-to-Out)The panel's full out-to-out width, before accounting for overlap.

Side Lap WidthHow much of each panel's width overlaps the adjacent panel along its side lap.

Panels neededThe tool computes the panels needed from those figures and shows the formula, its sources, and a confidence rating alongside it.

Total Roof Width	Panels needed (panels)
40 ft	13
60 ft	19
80 ft	25
100 ft	31
120 ft	37

Total Roof Width

Panels needed (panels)

40 ft

60 ft

80 ft

100 ft

120 ft

Frequently asked questions

Why does a shallower roof need more overlap, not less?

Because water climbs. On a steep roof a lap sheds almost immediately; as the pitch flattens, rain driven by wind travels UP the sheet against gravity, and it will get past a short end lap and run out on the inside. So the end lap grows as the pitch falls, and below the profile maker’s minimum pitch no lap length is enough and the joint has to be sealed or the sheet run in one unbroken length. The side lap behaves differently again: it is measured in whole RIBS rather than in millimetres, because the sheets only nest where the profile repeats, so the material lost sideways comes in fixed steps and a half-rib of extra cover is not available to be bought.

Why subtract the side lap width from the panel's full width?

Each panel overlaps the next one along its side lap, so only the net (non-overlapped) width actually adds new coverage across the roof — using the full out-to-out panel width would undercount how many panels are needed.

Does this calculation also cover end lap overlap?

No — this calculator only accounts for side lap overlap across the roof width. If a panel run is longer than one available sheet length, the end lap needed to join sheets end-to-end is a separate calculation not included here.

What happens if I enter a side lap width of 0?

The net coverage width becomes equal to the full panel width, which is the same as assuming no overlap between adjacent panels — this will understate the number of panels an overlapped installation actually needs.