How the estimates are calculated
Transparent area, coverage and packaging rules. Inputs and product specifications remain your responsibility.
Paint
Rectangular wall area is 2 × (length + width) × height. Actual opening deductions affect walls, not ceilings. Assigned ceiling area is length × width. For each product, combine the area × coats ÷ coverage-per-coat values, then apply its entered allowance. Subtract usable matching paint owned, and round the shortage upward to full cans. Zero shortage means zero cans.
Flooring
Combine non-overlapping rectangular floor areas for the same assigned product. Multiply by one plus the entered allowance fraction. Round planned area divided by box coverage upward, then subtract confirmed usable whole boxes. The result is never negative. Partial boxes and offcut reuse are outside this first model.
Wallpaper
For each rectangular room, count two length walls and two width walls separately: 2 × ceil(length/roll width) + 2 × ceil(width/roll width). Count all complete-height strips without opening deductions or partial-width reuse. Free-match cut length is height plus entered total trim. Straight-match cut length rounds this upward to a whole repeat. Deduct confirmed roll-start allowance from physical roll length and round strips-per-roll downward. A roll unable to supply one strip is an error. Round total strips divided by strips per roll upward, add explicit spare rolls, then subtract confirmed matching whole rolls owned.
A product group uses one height for wallpaper; mixed heights need separate entries and may produce a more conservative result. The model does not generate or optimise a cutting plan. Offset, half-drop and murals are blocked.
Rounding, units and prices
The core model uses decimal arithmetic with 40 significant digits. Display rounding does not change the original project values. Feet use the exact 0.3048 m factor; US liquid gallons use 3.785411784 L. The site does not use imperial gallons. Purchase counts are whole packages; material price is packages to buy × the entered price of the same package. Changing currency changes the label, not the numeric price.
Grouping and errors
A product ID defines a group. Products with matching text names are not automatically merged. Blank required inputs remain unknown, including allowance and owned stock. If one assigned group has an error, the complete material plan is marked incomplete and its export and print actions are disabled. Other valid groups may still be shown to help you edit.
Verification and changes
Published examples are synthetic arithmetic fixtures. Model tests and browser checks are recorded in the project release report. They are not a site survey, a manufacturer endorsement or real purchase validation. This first method version was prepared on 11 October 2026 with AI assistance. Corrections can be sent through the contact page.
Review reused modules and licences.
Sources and scope
For definitions of wallpaper match, repeat and packaging, see Brewster's product properties and Graham & Brown's wallpaper FAQ. Product instructions take precedence over generic examples. Unit conversions use the exact international foot (0.3048 m) and US liquid gallon (3.785411784 L); see NIST conversion factors.