Loan Metal Roofing Estimator
Metal panels are ordered by the piece and cut to length — the count depends on the panel's coverage width, not its full width, and that one distinction ruins more orders than any other. Enter the building and pitch: get panels per slope, panel length, screws and ridge.
For a simple gable roof: two slopes, panels running eave to ridge. Hips and valleys need a panel layout from the supplier — and usually 10–15% more metal. Panel length shown is the slope length; add your eave overhang.
How it works
Panel count is eave length ÷ coverage width per slope — a 36-in ag panel covers 36 in, but a 16-in standing-seam panel covers 16, which is why the same 40-ft eave takes 14 ag panels or 30 seam panels per slope. Panel length is the slope length: half the span times the pitch factor √(1 + (rise/12)²). Screws for exposed-fastener panels run about 80 per square (a square = 100 sq ft of roof); standing seam hides its fasteners in clips, roughly one clip per 18 in of seam.
Formula & worked example
Formula: Slope length = (span ÷ 2) × pitch factor √(1 + (rise ÷ 12)²); true roof area = length × span × factor. Panels per slope = ceil(eave length × 12 ÷ panel coverage width in inches); two slopes. Screws ≈ 80 per square (100 sq ft) for exposed-fastener panels.
Worked example: A 40 × 30 ft roof at 6/12 with 36-in panels: 14 panels per slope, 28 total at about 16.77 ft long, 13.42 squares, roughly 1,074 screws and 40 ft of ridge cap.
When to use this
- You are ordering metal panels for a barn, shop, cabin or house gable roof.
- You are comparing ag-panel and standing-seam quotes panel by panel.
- You need the screw count before the fastener order goes in.
How to use it, step by step
- Enter building length (eave) and width (span).
- Pick the pitch from the plans or the Roof Pitch Calculator.
- Choose the panel system by coverage width — 36 in ag or 16/12 in seam.
- Order panels by count and confirmed cut length; note screws and ridge separately.
What the inputs mean
| Input | What it is | Typical values |
|---|---|---|
| Building length | Eave length the panels run along | 24–60 ft typical outbuildings |
| Building width | Span across the gable | 20–40 ft typical |
| Pitch | Rise per 12 | 3/12 minimum for most panels; 6/12 common |
| Panel coverage | Net width each panel covers after the lap | 36 in ag; 16 or 12 in standing seam |
Another worked example
A smaller shop: 30 × 24 ft at 4/12 with 36-in ag panels. Slope length 12.65 ft, 10 panels per slope (20 total), 7.59 squares of roof, about 608 screws and 30 ft of ridge cap — a one-trailer materials run.
Frequently asked questions
How many metal panels do I need for a 40 × 30 roof?
At 6/12 with 36-in panels: 14 panels per slope, 28 total, each about 16.77 ft long (half the 30-ft span, pitched). The roof is 13.42 squares and takes roughly 1,074 exposed-fastener screws.
How long are the panels on a 30 × 24 roof at 4/12?
The slope runs 12.65 ft (half of 24 ft × the 1.054 factor), so panels cut around 12.7 ft plus overhang. That roof takes 10 panels per slope in 36-in coverage — 20 total.
Standing seam or exposed fastener?
Exposed-fastener (ag) panels are cheaper and DIY-friendly, but their screws have rubber washers that age in 15–20 years. Standing seam hides every fastener, costs roughly double in material, and is the 40-year answer. Panel count differs because coverage widths differ — compare installed totals, not panel prices.
How many screws per square?
Plan on about 80 screws per square for exposed-fastener panels over purlins or deck, per typical fastening patterns — more in high-wind zones. They come in bags of 250; the estimator's count rounds your order sensibly.
Can metal go over old shingles?
Often yes — over one layer, ideally on furring strips — which saves the tear-off. Check local code and the panel maker's spec, and weigh the saving against the chance to inspect and re-deck.
💲 Metal vs shingle, priced out?
Panels counted, compare the installed totals: the Roof Replacement Cost Estimator prices metal against asphalt and architectural shingles for the same roof.
What gauge metal should I buy?
29-gauge is the agricultural standard and the price leader; 26-gauge is the residential upgrade that resists hail dents and foot traffic better. Standing seam usually runs 24–26 gauge. Panel count does not change — price and lifespan do.
Do I need underlayment under metal?
Yes — high-temperature ice-and-water or synthetic underlayment over the deck (or over purlins per the panel spec). It is also the condensation management layer, which matters more on metal than on shingles.