Enter the roof length, the building width, the pitch and the overhang, and choose the panel coverage width. The calculator tells you how many panels you need, how long to order them, and how much trim to buy.
Extra and cost
Panel coverage is the width each panel covers once overlapped, not the full panel width. Fasten panels to the maker's pattern.
How the calculator works
- Panel length (gable roof) = (half the building width + overhang) × pitch factor
- Panels per side = roof length in inches ÷ panel coverage width, rounded up
- Total panels = panels per side × 2 for a gable roof, plus a little extra
- Trim: ridge cap along the ridge, eave trim along both eaves, and gable trim up each rake
Worked example
A building 40 ft long and 24 ft wide, with a 4/12 gable roof, a 12 inch overhang and 36 inch coverage panels:
- Panel length: (12 + 1) × 1.054 = 13 ft 8½ in, so order 13 ft 9 in
- Panels: 480 ÷ 36 = 13.3, so 14 per side, 28 in total, or 30 with 5 percent extra
- Panel area: about 1,233 square feet, or 12.3 squares
- Trim: 40 ft of ridge cap, 80 ft of eave trim and about 55 ft of gable trim
Coverage width
Metal panels overlap, so what matters is the coverage width, not the full width of the sheet.
- Exposed-fastener panels, such as many ribbed steel panels, often cover 36 inches.
- Standing seam panels are narrower, often 12 to 18 inches, with hidden fasteners.
Use the coverage figure from your supplier’s product sheet.
Ordering tips
- Panels are usually cut to length at the factory. Ask your supplier exactly how they want the length measured, including any gap at the ridge and the overhang at the eaves.
- Minimum pitch depends on the panel system. Many exposed-fastener panels need at least 3/12. Check the maker’s instructions.
- Fasten panels following the maker’s screw pattern for your wind zone.
To price a new metal roof, use the roof replacement cost calculator.
Frequently asked questions
How many metal roof panels do I need?
Divide the roof length in inches by the panel coverage width, round up, and double it for a gable roof. Add a few percent extra.
How do I calculate metal roof panel length?
Add half the building width and the overhang, then multiply by the pitch factor for your roof pitch.
How many squares of metal roofing do I need?
Multiply the number of panels by the coverage width in feet and the panel length, then divide by 100.
How wide is a metal roof panel?
Many common ribbed panels cover 3 feet. Standing seam panels are usually 12 to 18 inches.
Can metal roofing go over shingles?
Sometimes, depending on local code and the panel maker’s rules. Many installers add underlayment or purlins first. Check before you buy.
Results are estimates for planning. Follow the panel maker’s instructions. See How We Calculate for the formulas we use.
Guides for this project
Roofing & SidingRoof Pitch Chart: Common Roof Pitches Explained (4/12, 6/12, 8/12 and More)Roof pitch is how many inches a roof rises for every 12 inches it runs across, written as…Read the guide →7 min read
Roofing & SidingMetal Roof vs Shingles: Lifespan, Cost Factors, Pros and ConsA metal roof usually lasts 40 to 70 years, stands up well to wind, fire and snow, and…Read the guide →13 min read
Roofing & SidingHow Long Does a Roof Last? Shingles, Metal and MoreMost roofs last 15 to 30 years with asphalt shingles, 40 to 70 years with metal, and 50…Read the guide →9 min read