How this metal roof calculator works
Metal is ordered as discrete panels, not square feet — so the count comes from the ridge and the cut length comes from the slope:
panel length = (width ÷ 2) × √(1 + (pitch/12)²) · eave to ridge, one piece
Screws follow the roof’s squares at about 80 per square, underlayment at 10 squares a roll, and the cost is figured on the ordered panel area plus waste. At the defaults — a 40 × 30 ft roof at 4/12 in 36 in panels — that’s 28 panels cut 15′-9 3/4″ and about $4,184; the line-by-line math is in the panel math section below.
What’s in a metal roof system?
A metal roof is panels plus a kit of trim and closures — and the trim is where the roof actually keeps water out. The pieces, deck to ridge:
Deck and underlayment
Solid sheathing on a house, or open purlins on a barn. Over a deck goes a high-temp synthetic underlayment — metal runs hot, and standard felt cooks. The roof sheathing calculator counts the deck sheets.
Panels
The field metal, run eave to ridge in one length so there are no horizontal laps to leak. Coverage width — 36, 24 or 16 in depending on profile — sets how many panels the ridge takes.
Fasteners
Exposed-fastener panels use washered screws driven on a grid into the deck or purlins; standing seam clips hide underneath and let the metal move. Either way the fastener is a spec item — the panel maker’s screw is not the same as the bin screw.
Trim and flashing
Ridge cap, eave and rake trim, valley metal, and wall/chimney flashing — sold by the 10 ft stick, and a real line of the budget this calculator doesn’t count. Every trim piece has a matching closure.
Closures and sealant
Foam or metal closure strips fill the ribbed gaps at eaves and ridge so wind, water and wasps stay out, bedded in butyl tape. Skipping them is the classic screw-down leak.
Which metal roof profile and metal?
Two choices set the price: the profile (how the panel is formed and fastened) and the metal (what it’s made of). Profile first:
- Corrugated: the wavy classic, 36 in coverage, exposed screws — cheapest, quickest, barn-and-shed default. Wants 3/12+.
- Ribbed / R-panel (5V, PBR): trapezoidal ribs, 24–36 in coverage, exposed screws — the residential-agricultural workhorse, a step up in stiffness and looks.
- Standing seam: raised interlocking seams, hidden clips, 16–18 in coverage — no exposed holes, the premium look, and the only profile that reaches near-flat pitches.
- Metal shingles / stone-coated: panels stamped to mimic shingle or tile — the curb-appeal option, priced and counted differently from run panels.
Then the metal: galvanized or Galvalume steel is the value standard; aluminum resists salt for coastal roofs; copper and zinc are the lifetime architectural metals at architectural prices. Thickness matters too — 29-gauge for outbuildings, 26-gauge or heavier for houses and hail country.
| Profile | Coverage | $/ft² |
|---|---|---|
| Corrugated | 36″ | $1.50–3.50 |
| Ribbed / R-panel | 24–36″ | $2.50–5 |
| Standing seam | 16″ | $4–8 |
| Stone-coated steel | varies | $4–7 |
How much does a metal roof cost by size?
Table 2 runs common footprints through the engine at the default corrugated profile — panels only, no trim or labor.
| Footprint | Panels | Cost |
|---|---|---|
| 30 × 24 ft | 20 | $2,391 |
| 40 × 30 ft | 28 | $4,184 |
| 50 × 30 ft | 34 | $5,080 |
| 60 × 36 ft | 40 | $7,172 |
| Factor | Metal | Shingle |
|---|---|---|
| Lifespan | 40–70 yr | 15–25 yr |
| Material $/ft² | $1.50–8 | $1–1.50 |
| Min pitch | ½–3/12 | 2/12 |
| Snow / fire | Sheds / Class A | Holds / varies |
How to measure a roof for metal panels
The count comes off the ridge and the cut off the slope, so two measurements drive the whole order. Dimension fields take feet-inches (40, 40 ft 6 in) or metric (12 m).
- Measure the ridge length including gable overhangs — this ÷ panel coverage sets the panels per side.
- Measure the eave-to-eave width including overhangs. Half of it, stretched by the pitch, is the panel cut length.
- Get the pitch with a level and tape or the roof pitch calculator — and confirm it’s above your chosen profile’s tested minimum.
- Pick the coverage width for your profile — 36 in corrugated, 24 in ribbed, 16 in standing seam — the calculator recounts instantly.
- Leave waste at 5% for a simple gable; raise it for hips, valleys and lots of trim cuts, which eat metal faster than shingles.
- Enter your $/ft² for the chosen profile and metal, and remember the panel price is only part of a metal roof — the trim list follows.
Worked example: metal panels for a 40 × 30 ft roof
The defaults, worked line by line — 1,200 ft² footprint at 4/12, 36 in panels, 5% waste, $3/ft²:
multiplier @ 4/12 = √(1 + (4÷12)²) = 1.054
roof = 1,200 × 1.054 = 1,265 ft² = 12.65 squares
cut length = (30 ÷ 2) × 1.054 = 15.81 ft = 15′-9 3/4″
panels/side = (40 × 12) ÷ 36 = 13.3 → 14 → 28 panels
ordered = 28 × 15.81 × 3 = 1,328 ft²
screws = 12.65 × 80 × 1.05 = 1,063 · underlayment 2 rolls
cost = (1,328 × 1.05) × $3 = $4,184
Two field notes fall out of the math. Panels per side round up hard — 13.3 becomes 14, so that last panel is a rip, and its offcut is your waste. And the ordered area (1,328 ft²) runs above the roof area (1,265 ft²) before waste is even added, because whole panels overhang the rake slightly; that’s real metal, not double-counting.
What this metal roof estimate doesn’t include
The calculator prices field panels, screws and underlayment. On a metal roof the trim is a big slice of the budget — list it:
- Trim and flashing. Ridge cap, eave, rake, valley and wall trim by the stick — commonly 20–30% of the panel cost on a simple roof, more with valleys.
- Closures and sealant. Foam or metal closures and butyl tape at every eave and ridge.
- Furring / battens. If you’re going over shingles or open framing.
- Snow retention. Snow guards or rails where sliding snow threatens doors, walks or gutters.
- Tear-off. Stripping the old roof, if you’re not going over it.
- Pipe boots and vents. Metal-specific boots that survive the heat cycling.
- Labor. The bigger half — installed metal typically runs $10–20 per ft², panels included, and standing seam sits at the top.
Metal roof FAQ
How many metal roofing panels do I need?
Ridge length ÷ panel coverage width, per side: the default 40 ft ridge in 36 in panels is 13.3 → 14 panels a side, 28 total, each cut 15′-9 3/4″ eave to ridge at 4/12 on a 30 ft wide roof. Change the profile and the count re-runs.
How much does a metal roof cost?
Material for the default 1,200 ft² footprint runs about $4,184 in panels at $3/ft² with waste. By profile in 2026: corrugated $1.50–3.50/ft², ribbed $2.50–5, standing seam $4–8 — and installed metal roofing typically quotes at $10–20 per square foot, most of it labor and trim.
How long should metal roof panels be?
One piece, eave to ridge — 15′-9 3/4″ for the default roof — because horizontal laps are where screw-down roofs leak. Suppliers cut to the inch; keep panels under about 40 ft for shipping and thermal movement.
What roof pitch does metal roofing need?
Most exposed-fastener panels want 3/12 or steeper; standing seam with mechanically seamed ribs goes as low as ½/12 by manufacturer spec. Below those numbers water sits on the laps — check the panel’s tested minimum, not the metal itself.
How many screws per square of metal roofing?
About 80 per square (100 ft²) for exposed-fastener panels on the common 24 in purlin/screw grid — roughly 1,063 for the default roof with waste. Buy the washered screws the panel maker specs; ordinary screws weep at the washer in a season.
Can you put a metal roof over shingles?
Often yes — one layer of sound shingles, with the code’s reroof rules met (IRC R908) — over furring strips or a slip sheet so the ribs don’t telegraph and the two surfaces don’t abrade. It saves tear-off, but hides the deck condition and can trap heat; many installers still strip first.
Are metal roofs loud in the rain?
Not on a house — over solid sheathing and underlayment the sound is close to a shingle roof. The drum-on-a-barn reputation comes from panels screwed straight to open purlins with nothing behind them. Solid deck plus synthetic underlayment is the quiet build.
Is a metal roof worth it over shingles?
Metal costs 2–3× shingle material but lasts 40–70 years against 15–25, sheds snow, and drops cooling bills under light colors. The break-even usually lands around the second shingle roof you didn’t buy.
Sources and standards
The slope limits and coverage figures here come from the metal roofing industry’s own references:
- IRC R905.10: metal roof panel requirements — slope minimums (3/12 lapped, lower for sealed and standing seam) and deck/underlayment rules.
- IRC R908: the reroofing rules governing metal-over-shingles.
- MCA guidance (Metal Construction Association): panel coverage, fastener and closure practice behind this page.
- Manufacturer panel spec sheets: exact coverage width, screw pattern and tested minimum pitch — the panel maker governs whenever it differs from these averages.
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