About this calculator
This calculator counts profiled metal roof sheets — trapezoidal or tile-effect — for a symmetric two-slope (gable) roof: how many sheets each slope needs, the length to order them in, the ridge caps, the verge (gable) trims and the roofing screws.
Sheets are laid side by side along the roof, each one running from the eaves to the ridge in a single length. Two widths matter and they are not the same: the total width is what the sheet measures; the effective cover width is what it covers once it overlaps its neighbour. The count uses the cover width; the area you pay for uses the total width.
The building is described exactly as in the gable roof calculator: the building length along the ridge and the span wall to wall, plus the gable overhang at each end and the eaves overhang (measured horizontally) on each side. The pitch is an angle or a rise per run. If you already know the slope length from the eaves edge to the ridge, you can enter it directly instead. The sheet's own overhang past the eaves edge, into the gutter, is a separate input.
Formula
roof length = building length + 2 × gable overhang (gable edge to gable edge)
pitch = given angle, or atan(rise / run)
slope length = given, or (span / 2 + eaves overhang) / cos(pitch)
(span wall to wall; eaves overhang horizontal, each side)
net sheet length = slope length + sheet overhang past the eaves edge
ordered length = net length, or ceil(net length / module) × module (module > 0)
sheets per slope = ceil(roof length / effective cover width)
sheets total = 2 × sheets per slope
last-sheet excess = sheets per slope × cover width − roof length
net roof area = 2 × roof length × slope length
sheet area bought = sheets total × total width × ordered length
ridge caps = ceil(roof length / cap effective length)
verge trims / edge = ceil(net sheet length / trim effective length)
verge trims = 4 × trims per edge (2 gables × 2 slopes)
screws (net) = ceil(screws per m² × net roof area)
screw reserve = ceil(screws (net) × reserve %)
screw packs = ceil((net + reserve) / pack size)
Every count rounds up. Verge trims are counted per edge: an offcut from one gable is not assumed to finish another. Screws are counted on the net roof area — eaves edge to ridge on both slopes — not on the sheet area bought.
Worked example
Defaults: a 10 m building with a 300 mm gable overhang at each end, a 5 m slope, sheets overhanging the eaves edge by 50 mm, a 1180 mm sheet covering 1100 mm, no module, 1.9 m effective caps and trims, 7 screws per m² with a 5 % reserve in packs of 250.
roof length = 10 000 + 2 × 300 = 10 600 mm
net sheet length = 5000 + 50 = 5050 mm (ordered as is)
sheets per slope = ceil(10 600 / 1100) = ceil(9.64) = 10 → 20 sheets
last sheet excess = 10 × 1100 − 10 600 = 400 mm past the gable
net roof area = 2 × 10.6 × 5 = 106 m²
sheet area bought = 20 × 1.18 × 5.05 = 119.18 m²
ridge caps = ceil(10 600 / 1900) = ceil(5.58) = 6
verge trims = 4 × ceil(5050 / 1900) = 4 × 3 = 12
screws = 7 × 106 = 742, + ceil(37.1) = 38 = 780 → 4 packs of 250
Entered instead as an 8 m span wall to wall with a 500 mm eaves overhang at
35°, the horizontal run to the eaves edge is 8000 / 2 + 500 = 4500 mm and
the slope is 4500 / cos 35° = 5493 mm; with a 350 mm module the 5543 mm net
sheet is ordered as 16 × 350 = 5600 mm. A rise of 700 per 1000 run gives
4500 × √(1 + 0.7²) = 5493 mm as well (34.99°).
FAQ
Why is the effective cover width smaller than the sheet? Each sheet overlaps its neighbour by one or more ribs. That lap is part of the sheet you buy but covers nothing new, so the sheet count divides the roof length by the cover width, never by the total width.
What is the module step? Tile-effect sheets are pressed in steps of one tile row, so they can only be made in certain lengths. If your product has a module, enter it and the sheet length is rounded up to the next multiple. How the length is built from modules (and whether there is an extra fixed length at the eaves) is product-dependent; check the orderable lengths with the manufacturer. Trapezoidal sheets are usually cut to any length: leave the step at 0.
Are these the same inputs as the gable roof calculator? Yes: building length, span (wall to wall), eaves overhang (horizontal), gable overhang and pitch mean exactly the same there and here, so you can type the same figures into both. The slope length this calculator uses is the one the gable roof calculator reports (ridge centreline to the eaves edge).
I opened an older saved link and the eaves overhang shows 0 — why? Older versions asked for the span between the eaves edges, not wall to wall. A saved link keeps its result: that eaves-to-eaves width is carried over as the span with a 0 eaves overhang, which describes the same roof outline. If you know the wall-to-wall span and the overhang, enter them — the sheets stay the same as long as span + 2 × overhang is unchanged. Likewise the old roof length becomes the building length with a 0 gable overhang.
How far should sheets overhang the eaves? Far enough to drip into the gutter; the manufacturer's fixing instructions give the figure for your profile. The 50 mm default is a placeholder, not a recommendation.
Where do the screws per m² come from? From the sheet manufacturer: the fixing pattern depends on the profile, the batten spacing and the wind exposure. Manufacturers typically quote around 6–8 per m² for a standard roof; enter your product's figure. This calculator does not do a wind-load fixing design.
What if the sheets would be too long to deliver? Set the maximum sheet length to your supplier's or site's limit. If a sheet is longer, the calculator warns you; the usual fix is two sheets per run with an end lap, which this calculator does not lay out.
Assumptions and limits
No standard is cited. The take-off is geometry and counting; cover widths, modules, cap and trim lengths and fixing densities are the manufacturer's. No standard covering this take-off was verified and none is invented.
Every product figure is an estimate you should replace: the 1100/1180 mm sheet widths, the module step, the 1900 mm cap and trim effective lengths, the 7 screws per m², the 5 % screw reserve, the pack of 250 and the 8 m maximum sheet length (a transport and handling limit, not a rule).
The roof is a symmetric gable with one sheet per run from eaves to ridge. Hips, valleys, dormers, roof windows, end laps and a gap at the ridge are not modelled. The sheets are assumed to cover the gable overhangs, so the roof length is the building length plus both gable overhangs.
The eaves overhang is horizontal, as in the gable roof calculator: it extends the run before the pitch is applied. The sheet overhang past the eaves edge is separate and measured along the slope. The 500 mm eaves and 300 mm gable overhang defaults are example values for your building, not recommendations.
No waste percentage is applied to sheets: they are made to length, and the only waste is the part of the last sheet that runs past the gable edge, which the calculator reports. Eaves trims, flashings, underlay, battens and snow guards are not counted.
The minimum pitch for a given profile is the manufacturer's; this calculator does not check it.