Metal roofing panel calculator

Metal panels are ordered by the piece, cut to your roof, so you need two numbers: how many panels across, and how long each one is. Both come out of this. The trap is the width — a panel that measures 37 in across only covers 32 in once it laps the one beside it.

Eave length of one roof plane Measure along the gutter line, including gable overhangs. Panels run up the slope, so this is the direction you count panels across. Roof planes of this size A plain gable is 2. A lean-to or shed roof is 1. Run the calculator once per size if your planes differ. Run from eave to ridge Horizontal distance, not the sloped distance — the pitch below converts it. On a symmetric gable this is half the building width. Roof pitch (rise per 12 in of run) Panel net coverage width Published coverage, not the width you measure across a loose panel. R-Panel/PBR 36 in. 7/8 in corrugated 32 in on a roof (37 in overall). 5V-Crimp 24 in (26 in overall). Snap-lock standing seam 12, 16 or 18 in. Panel overhang past the eave 1–2 in into a gutter, 2–3 in over a drip edge with no gutter. Added to the panel length, once per plane. Extra for waste and cuts % 0–5% on a plain gable, where panels are cut to length and only the last one gets ripped. 10–15% once you have hips, valleys or dormers, because every panel there is a diagonal cut.

Panels to order 31 panels

Length of each panel 15.82 ft Round up to the next inch your supplier rolls, then order that exact length.

Panels across one plane 14 panels

Actual roof surface 1,252 sq ft Pitch applied, before waste.

Total lineal feet of panel 490 ft Panels are usually priced per lineal foot — this is the number to quote.

Coverage width is not panel width

This is the one number that matters, and it is the one a supplier quote is most likely to leave ambiguous. A metal panel has to lap the panel beside it, so the width you measure across a loose sheet is always more than the width it covers on the roof.

Western States Metal Roofing publishes both figures for its 7/8 in corrugated panel: overall width 37 in, roof coverage 32 in (and 34.67 in on a wall, because walls lap one corrugation and roofs lap one and a half). Divide your eave length by 37 instead of 32 and you order 14% too few panels.

The other common profiles:

R-Panel / PBR — 36 in coverage, 1-1/4 in ribs at 12 in on centre. MBCI and McElroy Metal both publish the same figure.
5V-Crimp — 26 in overall, 24 in coverage.
Snap-lock standing seam — sold by coverage already. McElroy's Medallion-Lok comes in 12, 16 and 18 in.

If the supplier quotes you a single width, ask which one it is. If the answer is vague, ask for the coverage on a roof, not a wall.

Panels are cut to length, so order the length

Unlike shingles, metal panels are roll-formed to your dimension — Western States quotes 1 ft to 52 ft, McElroy up to 50 ft. So the goal is not "how many square feet" but "how many panels of exactly this length".

The length is the sloped distance from ridge to eave plus the overhang:

panel length = run × pitch multiplier + overhang

where the multiplier is √(1 + (rise ÷ 12)²) — 1.054 at 4/12, 1.118 at 6/12, 1.202 at 8/12. It is the same correction the roof shingle calculator uses, and it is just as easy to forget here.

Allow 1–2 in of overhang into a gutter, 2–3 in over a drip edge with none. Order one length for the whole plane; a run of panels that vary by half an inch is visible from the street.

Count panels per plane, not per roof

Round up each plane separately. A 40 ft eave at 36 in coverage is 13.3 panels, so 14. Two planes is 28. Add the two eaves first and you get 26.7, round to 27, and you are one panel short — that error grows with every plane on the roof.

The last panel on each plane is normally ripped down. That offcut is dead material, which is why even a simple gable is not a zero-waste job, and why the final panel is worth planning: a 4 in strip at the rake looks wrong, so many installers narrow the panels slightly across the whole run instead.

What this does not cover

Ridge cap, eave and rake trim, closure strips, sealant tape and screws are all separate, and they are what turns a pile of panels into a roof. Screw counts in particular vary from one manufacturer's pattern to another, so take them off the installation guide for the panel you actually buy.

Four assumptions live inside the numbers themselves.

The coverage width on this page is a roof figure. The same panel covers a different width on a wall: Western States publishes 32 in on a roof and 34.67 in on a wall for its 7/8 in corrugated, because the roof laps a corrugation and a half where the wall laps one. There is a single coverage field here, so if the same profile is running up a gable end or onto a wall, enter the wall figure and take that elevation off separately.

The pitch multiplier lengthens the panel and says nothing about the plan. A valley, a hip, a dormer or a turret gets the same answer as a plain rectangle with the same eave and run, and all the diagonal cutting those shapes force sits inside the waste percentage instead — which is exactly why that field jumps to 10–15% as soon as the roof stops being a simple gable. It is an allowance, not geometry.

Every plane is taken to be the same size, and the last panel is assumed to be ripped without complaint. The page will not tell you how wide that final strip lands, which is the thing installers actually plan the run around. Planes with different eave lengths or different runs need their own pass.

Nothing here checks the slope against the panel you chose. IRC R905.10.2 sets three different minimums: 3:12 for a lapped, non-soldered seam with no lap sealant, 1/2:12 for that same seam once sealant is applied to the manufacturer's instructions, and 1/4:12 for a standing-seam system. The pitch list on this page runs down to 1/12 because its job is to turn a run into a length, not to approve an assembly — at that slope only two of those three constructions are on the table, and the panel's own installation instructions can be stricter than the code.

One more: the panel length is treated as a single piece. If your run is longer than your supplier will roll, the roof needs an end lap, and neither the extra length nor the sealant at that joint is counted here.

Questions people ask

How wide is a metal roofing panel?

It depends which width you mean. A 7/8 in corrugated panel measures 37 in across but covers 32 in on a roof, because it laps one and a half corrugations. R-Panel and PBR cover 36 in. 5V-Crimp is 26 in overall and covers 24 in. Always estimate with the coverage width.

How many metal roofing panels do I need for a 24x24 garage?

With the ridge running along one 24 ft side and 36 in coverage panels, that is exactly 8 panels per slope, 16 in total — 24 ft divides evenly by 36 in, so nothing gets ripped and you need no waste allowance. Each panel is 12 ft of run times the pitch multiplier plus overhang, about 12.8 ft at 4/12, so order 13 ft.

What length metal roofing panels should I order?

The sloped distance from ridge to eave plus 1–2 in of overhang, in one piece if you can. Manufacturers roll to order up to about 50 ft. A single-length panel has no end lap, which is the joint most likely to leak.

How much waste should I allow for a metal roof?

Almost none on a plain gable, because panels are cut to length — 0 to 5% covers the rip on the last panel. Allow 10–15% once there are hips, valleys or dormers, where every panel meeting the diagonal is cut and the offcut is unusable.

Can metal panels go over existing shingles?

Often yes, and it is common on exposed-fastener re-roofs, but check two things: your local code on the number of permitted roof layers, and whether the panel needs purlins or a vented batten layer over the old surface. Screwing straight through lumpy shingles into thin decking is how fasteners back out.

Last reviewed 2026-07-31