Metal roofing calculator
Roof plane length, roof width, number of planes, panel coverage width, panel length and end lap: you get panels with waste, screws and trim.
Purchase quantity
21 panel
Net measurement: 1291.669 ft² · Waste 5 %
- Panels21 panel
- Self-drilling screws (6 per m²)3 box
- Ridge cap32.808 ft
- Rake / gable trim78.74 ft
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How it's calculated (visible formula)
columns = ceil(width ÷ coverage); rows = ceil((plane − lap) ÷ (panel − lap)); panels = columns × rows × planes
- Net geometric measurement, no waste.
- Adjustable waste % for cuts and breakage.
- Purchase rounded up to sellable units (boxes, bags, buckets, boards).
How to calculate it, step by step
- Measure plane length eave to ridge and roof width.
- Enter panel coverage width and length.
- Work out columns and rows with end lap.
- Multiply by planes and add waste.
- Add screws, ridge cap and trim.
Worked example: Two planes of 20 × 33 ft, 36 in coverage, 20 ft panels
- 33 ft ÷ 3 ft = 11 columns
- 1 row per plane
- 22 × 1.05 = 24 panels
→ About 24 panels (21 with 1 m coverage), screws and 33 ft of ridge cap.
Common mistakes
- Using full panel width instead of coverage.
- Short end laps on low slopes.
- Screws without neoprene washers.
Pro tips
- Start on the side opposite the prevailing wind.
- Fasten on the rib or flat per the maker's system.
- Use sealant tape on laps at low pitches.
- Add underlayment or condensation control over living space.
From calculation to quote
Add labour, overhead and your margin, and generate the professional PDF.
FAQs
- What is panel coverage?
- The width a panel covers once overlapped — 36 in for many ribbed panels.
- What end lap?
- 6–8 in; more below 3/12 pitch.
- How many screws per square?
- About 70–80 per 100 sq ft, depending on purlin spacing and wind zone.
- Minimum pitch for metal roofing?
- Often 3/12 for exposed-fastener panels; 1/2:12 for some standing seam.
- Standing seam or exposed fastener?
- Standing seam lasts longer with hidden fasteners; exposed fastener is cheaper.
- How much does metal roofing weigh?
- About 1–1.5 lb per sq ft.
Sources and standards
Maintained by Srikanta M · Formula v1.0.0 · Verified 2026-09-10 · Updated 2026-09-10 · Limits: quantity estimation, not structural design or site supervision.