How to use the metal roofing calculator
- Enter the eave length of one roof side.
- Enter the panel run: the length along the slope from eave to ridge, including the overhang. The rafter length calculator works this out from span and pitch.
- Enter the number of roof sides with the same dimensions.
- Enter the panel coverage width from the spec sheet: the width each panel covers after overlapping its neighbour, not the full sheet width.
Confirm the panel's coverage width with the manufacturer. It differs between profiles, and Decoratoradvice relies on the figure you enter.
Metal roofing formulas
Panels per side = eave length ÷ coverage width, rounded up
Panels = panels per side × number of sides
Panel length = panel run (eave to ridge, including overhang)
Area covered = eave length × panel run × sides
Worked example
A gable roof with a 40 ft eave on each side, a 16 ft panel run and 36 in coverage panels:
Panels per side: 480 in ÷ 36 in = 13.3, so 14
Panels: 14 × 2 = 28 panels, each 16 ft
Area: 40 × 16 × 2 = 1,280 sq ft
Ordering tips
- Many suppliers cut panels to length. Confirm the panel length with them, including any overhang at the eave.
- Order trim at the same time: ridge cap (about the ridge length), eave and gable trim, and closures, as listed in the manufacturer's installation guide.
- Fastener counts and patterns come from the manufacturer's guide for your panel and wind zone.
- For the same roof in shingles, compare with the roofing calculator.
Common mistakes
- Using the full sheet width. Overlap reduces the coverage width.
- Measuring the run horizontally. Panels follow the slope; use the sloped length.
- Mixing up sides on hip roofs. Hip roofs have triangular sides that need cut panels; plan them with the supplier.
Frequently asked questions
How many metal panels do I need for my roof?
Eave length ÷ coverage width per side, rounded up, times the number of sides. 40 ft at 36 in coverage is 14 per side.
How long should metal roof panels be?
The slope length from eave to ridge, plus the overhang at the eave, as recommended by the manufacturer.
What is panel coverage width?
The net width a panel covers once it overlaps the next one. It is on the panel spec sheet.
What is the minimum pitch for a metal roof?
It depends on the panel system. Manufacturers state a minimum pitch for each profile; check before ordering. The roof pitch calculator converts your roof to x/12.
Do I need gutters with a metal roof?
Most houses still need gutters; see the gutter calculator.
Key takeaways
- Panels per side = eave ÷ coverage width, rounded up.
- Panel length = slope length, including overhang.
- Use the coverage width, not the sheet width.
- Trim and fasteners follow the manufacturer's guide.