Wallpaper Roll Calculator mechanism

Model scope

The instrument cannot honestly claim to provide a waste estimate until a waste formula and its inputs are specified. Clarify whether repeat_waste is a fixed allowance or a pattern-repeat interval, define standard roll dimensions by market, and provide the missing wall-perimeter/roll-width strip-count calculation. Until then, label the result as an estimate of rolls based on precomputed strip count, not an exact requirement.

• The standard pattern-repeat cut length is usually ceil(wall_height/pattern_repeat)*pattern_repeat, not wall_height+repeat_waste. The stated formula is valid only if repeat_waste is explicitly defined as a fixed additional cut allowance per strip.
• No formula is provided for the claimed waste estimate.
• The formula assumes total_strips_needed is already calculated, but no formula is provided from wall dimensions, roll width, doors, windows, or openings.
• The 10-15% waste buffer in honest_label is not implemented or defined as an input; applying it before or after ceiling can produce different roll counts.
• US double-roll and EU-roll defaults are not universal dimensions, and usable roll length can differ from nominal roll length.

Units and conventions

• roll_length, wall_height, and repeat_waste must use the same linear unit before division.
• total_strips_needed must be a nonnegative integer, normally calculated as ceil(wall_perimeter/usable_roll_width) after accounting for openings and layout.
• roll_length must mean usable wallpaper length, excluding packaging, damaged material, or unusable selvage.
• repeat_waste must be a nonnegative length allowance per strip if this formula is retained; it must not be confused with the pattern-repeat interval.

Inspectable vector

One of 4 source-bound review vectors:

{
  "inputs": {
    "wall_perimeter_m": 16,
    "roll_width_m": 0.53,
    "wall_height_m": 2.4,
    "repeat_waste_m": 0.3,
    "roll_length_m": 10.05,
    "total_strips_needed": 31
  },
  "expected_outputs": {
    "strips_per_roll": 3,
    "rolls_required": 11
  },
  "working": "Cut length per strip = 2.4 + 0.3 = 2.7 m. Strips per roll = floor(10.05 / 2.7) = floor(3.7222...) = 3. Total strips from wall width = ceil(16 / 0.53) = ceil(30.1886...) = 31. Rolls required = ceil(31 / 3) = ceil(10.3333...) = 11."
}

Failure boundary

BREAK_CLAIMED · SELF_FLAGGED

A zero wall height combined with zero pattern repeat makes the effective strip length zero, causing division by zero and an undefined roll count; the calculator must reject the input.

Other records

Sources and evidence

These pointers bind the page to evidence. They do not grant authority or collapse verification into deployment.

• VERIFIED_LEDGER.json
• evidence-tranche3/tranche3-results.json
• BOUNDARY_HAZARD_CATALOG.json