How this estimate works
The width used to count columns is the cover width after the manufacturer’s side lap, not the sheet’s overall metal width. Record this value from the exact profile you plan to buy. Divide each plane’s eave width by that effective width and round upward; do not combine spare widths from separate roof planes unless a verified cutting layout permits it.
The length output is the actual measured slope from eave to ridge plus a user-entered allowance for approved overhang or end detail. This calculator assumes every column is covered by one full-length panel. The cited Classic Rib instructions state that the panels cannot be end lapped, so the calculator does not invent a multi-row end-lap rule. Check a supplier’s available manufacturing lengths against every cut length.
The extra-panels percentage is applied after the sum of full-length columns and rounded upward. It estimates count only; any spare panel length has to be specified to the supplier separately. Roof geometry, valleys, penetrations, trim, fasteners, structural adequacy, and safety are outside this panel-count estimate. Have an installer or supplier verify the order against the actual roof plan.
Keep a copy of your measurements and the product information used. Recheck both before ordering, especially after a layout or supplier change.
Read the full How to Measure Roof Planes and Count Full Length Metal Panels for measuring steps, worked examples, and common order mistakes.