Quick answer
Panels = ⌈roof width × 12 ÷ panel coverage width⌉. A 30 ft wide roof with 36 inch coverage panels needs 10 panels of 12 ft, 120 ft of panel in total.
Enter the roof width, panel coverage width and panel length. The calculator returns panels and total length. Use this metal roofing calculator to check your own figures.
Related tools: Roofing Calculator: Roof surface area and roofing squares from the footprint and pitch. Roof Pitch Calculator: Roof pitch as rise per 12 inches, angle, slope percent and rafter length factor. Roof Shingles Calculator: Squares and bundles of shingles for a roof area.
How to use the Metal Roofing Calculator
- Enter roof width to cover (ft) (above 0).
- Enter panel coverage width (in) (above 0).
- Enter panel length (ft) (above 0).
- Press Calculate to see the result, and use Reset to start again.
| Input | What to enter | Allowed values |
|---|---|---|
| Roof width to cover | A number, in ft | > 0 |
| Panel coverage width | A number, in in. Net width a panel covers | > 0 |
| Panel length | A number, in ft | > 0 |
Formula and method
Formula
panels = ⌈roof width × 12 ÷ coverage width⌉
IEEE-754 double precision; shown to the decimals indicated.
Panel coverage width is the net width after overlap, listed by the manufacturer. Plan geometry only; confirm quantities with your supplier and local code before ordering.
Worked examples
These examples are verified: each one is an automated test case that the live calculator must reproduce exactly.
Example 1
Inputs: Roof width to cover = 30; Panel coverage width = 36; Panel length = 12.
| Result | Value |
|---|---|
| Panels needed | 10 |
| Total panel length | 120 ft |
Example 2
Inputs: Roof width to cover = 24.5; Panel coverage width = 24; Panel length = 10.
| Result | Value |
|---|---|
| Panels needed | 13 |
| Total panel length | 130 ft |
The first line is the headline result (panels needed). Below it the metal Roofing Calculator lists total panel length, which describe the same case from other angles. IEEE-754 double precision; shown to the decimals indicated.
Coverage versus overall width
Panels overlap at the seams, so a panel sold as 38 inches wide may cover only 36 inches. Always use the coverage width. 360 inches ÷ 36 inches = 10 panels exactly.
Trim and fasteners
Ridge caps, flashing, drip edge and screws are separate. Panel length should span the roof slope with overhang. For long slopes you may need panels in two lengths.
How the result changes with roof width to cover
Holding every other input at the first worked example, this table changes only roof width to cover. It shows how sensitive the answer is to that one value; each row was produced by running this calculator.
| Roof width to cover | Panels needed | Total panel length |
|---|---|---|
| 15 | 5 | 60 ft |
| 30 | 10 | 120 ft |
| 60 | 20 | 240 ft |
| 120 | 40 | 480 ft |
What happens with invalid input
These messages are produced by the calculator itself, so you know what to fix.
- Roof width to cover: entering "0" shows "Roof width to cover must be greater than 0." beside that field and no result.
- Panel coverage width: entering "0" shows "Panel coverage width must be greater than 0." beside that field and no result.
Choosing between the Metal Roofing Calculator and similar calculators
Each row shows what a related calculator on this site asks for and what it returns, so you can pick the one that matches your question.
| Calculator | You enter | It returns |
|---|---|---|
| [Roofing Calculator](/construction/roofing-calculator/) | building length, building width and roof pitch | Roof area |
| [Roof Pitch Calculator](/construction/roof-pitch-calculator/) | i know the and value | Pitch |
| [Roof Shingles Calculator](/construction/roof-shingles-calculator/) | roof area, bundles per square and waste allowance | Bundles needed |
| [Roof Sheathing Calculator](/construction/roof-sheathing-calculator/) | roof area, sheet size and waste allowance | Sheets needed |
| [Ice and Water Shield Calculator](/construction/ice-water-shield-calculator/) | area to cover, coverage per roll and waste allowance | Rolls needed |
Background: construction estimates
Material quantities are geometry plus a margin. Calculate the exact volume or area, add an allowance for waste, spillage, cuts and uneven ground (calculator pages commonly mention 5 to 10 percent, a rule of thumb that varies by material and job) and round up to whole units. One cubic yard is exactly 27 cubic feet.
Suppliers often have minimum order sizes and may charge for small loads, so confirm quantities, product yields and local code with your supplier or a qualified estimator before ordering.
Assumptions and limitations
- Add trim and flashing separately
Quantities are estimates. Add allowances for waste and site conditions, and follow local codes and a qualified professional's instructions for structural or safety-critical work.
If a required value is empty, not a number, or outside its allowed range, the form marks that field with a message and shows no result instead of a misleading number. The automated checks deliberately try invalid entries for roof width to cover and panel coverage width to confirm this.
Frequently asked questions
Do I need to order extra?
Order one extra panel for cutting.
How do I find panel length?
Measure eave to ridge and add the overhang.
Does it include the pitch?
Use the slope length, not the horizontal run.
What does the Metal Roofing Calculator calculate?
Number of metal roofing panels across a roof width. It returns Panels needed and Total panel length.
What formula does the Metal Roofing Calculator use?
panels = ⌈roof width × 12 ÷ coverage width⌉. Panel coverage width is the net width after overlap, listed by the manufacturer.
What do I need to enter in the metal Roofing Calculator?
You enter Roof width to cover (ft), Panel coverage width (in) and Panel length (ft).
How is the result rounded or limited?
IEEE-754 double precision; shown to the decimals indicated. Add trim and flashing separately.
What is an example of a metal Roofing result?
With roof width to cover 30, panel coverage width 36 and panel length 12, the panels needed is 10.
Can I rely on this calculator for a decision?
Quantities are estimates. Add allowances for waste and site conditions, and follow local codes and a qualified professional's instructions for structural or safety-critical work. For this calculator in particular: Add trim and flashing separately.
Related calculators
- Roofing Calculator — Roof surface area and roofing squares from the footprint and pitch.
- Roof Pitch Calculator — Roof pitch as rise per 12 inches, angle, slope percent and rafter length factor.
- Roof Shingles Calculator — Squares and bundles of shingles for a roof area.
- Roof Sheathing Calculator — Sheets of plywood or OSB for a roof area.
- Ice and Water Shield Calculator — Rolls of ice and water membrane for an area.
- Gutter Length Calculator — Total gutter length and number of sections from your eave lengths.
Sources
- OpenStax, Prealgebra 2e (Rice University): perimeter, area, volume, circumference and the Pythagorean theorem
- NIST Special Publication 811, Guide for the Use of the International System of Units (SI), Appendix B conversion factors (international foot 0.3048 m, inch 25.4 mm, US gallon 3.785411784 L)
Content last reviewed 2026-11-04. Formulas and worked examples are checked by automated tests against independently computed values.