Sheet count across a plane is ceil(width ÷ effective cover). Width is ridge-direction including barges/verges, perpendicular to the ribs. Cover is after the side lap. Length is a different number (slope including eaves, +50 mm on this site).
The sheet calculator does that. Searcher version: how many sheets for a NZ roof.
Worked gable plane
7.200 m on 762 mm Dimond corrugate: 7.200 ÷ 0.762 = 9.45 → 10 sheets that plane, 20 on a symmetric gable. Using 851 mm overall: 8.46 → 9 per plane and a missing sheet.
8.4 m ÷ 0.762 = 11.02 → 12. 10.8 m ÷ 0.760 = 14.21 → 15.
Round up. 9.01 is 10 sheets. Confirm millimetres from the coil: Metalcraft corrugate 760, Hi Five 765 (sometimes 755), tray often not 300 — Dimond vs Metalcraft.
What this formula does not do
Hip ends are not a clean cover count; this engine switches toward area plus cutting waste (waste). Multi-section: round up per plane, never add widths then divide once (multi-section). Flashings are lineal metres, not extra sheets.
Pitch does not change how many sheets fit across the ridge. It changes length, min-pitch flags, and run checks.
Open the takeoff, read the cover used in the result, and match the coil tag before anyone rolls metal. NZMRM CoP and the product sheet still win.