Methodology
Formula & assumptions
Room shell
2 × (length + width) × height + optional ceiling
Base rectangular-room surface.
Net drywall surface
room shell + other measured surface − measured openings
Deductions and extra zones stay explicit.
Sheet target
net surface × (1 + waste %) ÷ sheet area
Rounded to whole sheets.
Tape
measured joint run × (1 + allowance) ÷ roll length
Uses measured joints rather than an invented area-to-joint rate.
Compound / screws / bead
net surface or measured corner run × editable project assumptions
Rates and package sizes remain visible inputs.