Understanding your result
The headline is the total panels, with the order lines (count × length) in the subtitle. The stats give the panels, the number of distinct lengths and the area of panel ordered. The breakdown lists each section’s slope and panel length, then its panel count, then the order lines grouped by length, and in stock mode the offcut.
The thing to use is the order lines: they are what goes on the supplier’s form, one line per length. The area of panel ordered is the figure for the screws calculator, and the eave and ridge lengths of the sections feed the trim calculator.
For a single rectangular roof the panel calculator gives the same answer with more explanation; this page exists for the roofs that are not rectangles. Standing seam uses the standing seam calculator for clips, but the cut list logic is the same with the seam spacing as the coverage width.
How we calculate this
Each section is run through the same arithmetic as the panel calculator, then the lengths are collected: two sections that happen to produce the same length (the two planes of a gable roof, or two matching dormers) merge into one order line. In stock mode each section’s length is rounded up to the next stock size before merging, which is why two sections of 18 feet 1 inch and 19 feet 6 inches both become 20-foot panels.
The run of each section is measured from its eave to its ridge (or to the wall it meets) in plan, including the eave overhang, and the pitch is that section’s own. The roof area calculator gives the areas if you want to check the total against the roof, and the panel maths guide walks through an L-shaped roof with a porch section by section.
The assumptions behind the numbers
| Assumption | Default | Where it comes from |
|---|---|---|
| Sections | 2 of 40 ft eave and 16 ft run at 6/12 | The site’s example gable roof; sections 3 and 4 default to a 20 ft porch at 8 ft run |
| Coverage width | 36 in | Standard ribbed panels; 24 for corrugated, 12 to 18 for standing seam |
| Eave overhang | 2 in | Manufacturers’ guides (1 to 2 in past the drip edge) |
| Stock lengths | 8, 10, 12, 14, 16, 20, 24 ft | What lumber yards commonly rack |
| Waste | 5% | Estimating practice; 0 for plain sections, 10 to 15 for hips and valleys |
| Length rounding | up to the next inch | Panels are cut to the inch |
Assumptions last reviewed October 7, 2026.
The calculator does not measure the roof, does not handle more than four sections (run it twice), and applies one waste figure to every section. It does not count trim, closures or screws. The measuring guide covers getting each section’s run and pitch without a ladder.
Two worked examples
A plain gable roof, cut to length
Two sections of 40 feet of eave, 16 feet of run at 6/12, 36-inch panels, 2-inch overhang, 5% waste.
- Slope: 16 × 1.118 = 17 ft 11 in; panel: 18 ft 1 in
- Panels per section: 480 ÷ 36 = 13.3, so 14; with waste 15
- Order: 30 panels at 18 ft 1 in; 1,628 sq ft of panel
One line on the order. The 5 percent waste adds a panel per side; on a plain gable it could be zero.
The same roof plus a porch, from stock lengths
Four sections: the two main planes as above, plus two 20-foot porch planes at 8 feet of run on a 4/12 pitch; stock lengths, no waste.
- Main planes: panel 18 ft 1 in, rounded up to 20-ft stock; 14 panels each, 28 in all, leaving 26.8 ft of offcut per plane
- Porch planes: slope 8 × 1.054 = 8 ft 5 in; panel 8 ft 8 in, rounded up to 10-ft stock; 240 ÷ 36 = 6.7, so 7 each, 14 in all
- Order: 28 × 20 ft and 14 × 10 ft, 42 panels, 2,100 sq ft; 72 ft of offcut in total
Seventy-two feet of offcut is three and a half panels’ worth of metal paid for and thrown away. Cut to length, the same order is 28 × 18 ft 1 in and 14 × 8 ft 8 in.
Where to find your inputs
Eave length per section. Edge to edge along the bottom of the plane, including rake overhangs; for two identical planes, enter their combined eave as one section.
Run per section. From the eave (drip edge) to the ridge or wall in plan, measured on the ground or the plan, including the eave overhang.
Pitch per section. Each plane’s own pitch; porches and additions are often shallower than the main roof. One unit (rise per 12 or degrees) applies to all sections.
Lengths mode. Cut to length for a metal roofing supplier; stock for a lumber yard’s rack.
Common mistakes
- One length for the whole roof. A porch at 4/12 and a main roof at 6/12 need different panels. Separate sections.
- Measuring the run to the wall instead of the eave. The panel runs to the drip edge, overhang included.
- Mixing up the two planes of a hip roof. The end planes of a hip roof are triangles with a shorter eave and the same run; enter them as their own section with a 15 percent waste.
- Stock lengths from a supplier that cuts. Ask; most cut to the inch and the offcut vanishes.
- Forgetting the dormers. Each dormer face is a tiny section with its own short panels. Four sections is usually enough; run the calculator twice if not.
- Unlabelled bundles. Three lengths on one pallet take an hour to sort on the roof. Label by section.
Questions people ask
- What is a cut list for metal roofing?
- A list of panel lengths and how many of each, because metal panels are made to length for each roof plane. For a gable roof with two 40-foot planes at 16 feet of run on a 6/12 pitch, the list is one line: 30 panels at 18 feet 1 inch. Add a porch at 4/12 and a dormer and it becomes three lines with three lengths.
- How do I measure a roof section for a cut list?
- Each section is one roof plane (or a pair of identical planes): its eave length from edge to edge, its run from the eave to the ridge in plan including the overhang, and its pitch. The panel length is the run times the pitch factor plus the eave overhang; the count is the eave divided by the coverage width. The measuring guide covers getting the run and pitch from the ground.
- Should I order panels cut to length or in stock lengths?
- Cut to length, nearly always: most metal roofing suppliers cut to the inch at the same price per foot, so there is no offcut to pay for or carry. Stock lengths (8, 10, 12, 14, 16, 20 and 24 feet) are what a lumber yard keeps on the rack; use that mode if that is where you are buying, and the calculator shows how much offcut each section leaves.
- How should panels for hips and valleys be ordered?
- At the full length of the section, with a waste allowance of 10 to 15 percent on that section; the panels are then cut on the diagonal on site. There is no shorter length to order, because every panel along a hip is a different length. The calculator applies one waste figure to all sections; enter the figure for the worst of them.
- Can I order one long panel for two sections?
- Only if the two sections are in line on the same slope, which is rare. A porch roof at a different pitch, a dormer face or a wing at right angles each need their own length, and a panel ordered for the longest section and cut for the others wastes the difference on every panel.
- What is the longest panel I can order?
- About 40 feet by truck; beyond that, suppliers roll-form on site or ask you to lap two panels 6 inches over a purlin. The calculator flags a section whose panel is longer than the longest stock length in stock mode, and the panel calculator notes panels over 40 feet.