Methodology
Deterministic, versioned arithmetic. No AI for numbers. Money in whole minor units (USD cents), metric, and a strict split between markup — % on cost — and margin — % on price.
Common rules
- buy_qty = net × (1 + waste), with adjustable waste.
- Purchase rounded UP to sellable units (boxes, bags, buckets, boards).
- Invalid inputs (negatives, zero where not allowed, NaN, Infinity, mixed units) are rejected with a clear error.
- Configurable tax per country profile (USA default 0% — no federal sales tax; set your state rate).
Formulas per calculator (v1.0.0 · verified 2026-09-10)
- Wall & ceiling area calculator — see formula on its page
net = Σ(length × height) + ceiling − openings; buy = net × (1 + waste) - Paint calculator — see formula on its page
net_litres = area ÷ coverage × coats; buy = net × (1 + waste); buckets = ceil(buy ÷ bucket) - Tile calculator — see formula on its page
net_pcs = area ÷ (width × length); boxes = ceil(area × (1+waste) ÷ m² per box) - Adhesive & grout calculator — see formula on its page
kg = area × consumption; bags = ceil(kg × (1+waste) ÷ bag) - Drywall calculator (boards) — see formula on its page
net_boards = area × sides ÷ (width × length); buy = ceil(net × (1+waste)) - Framing & screws calculator — see formula on its page
tracks = ceil(2L ÷ 3); studs = floor(L ÷ spacing) + 1; screws ≈ 25 × m² - Brick calculator — see formula on its page
pcs = area × pcs/m²; buy = pcs × (1+waste) - Concrete block calculator — see formula on its page
pcs = area × 12.5; buy = pcs × (1+waste) - Mortar calculator — see formula on its page
kg = m² × kg/m²; bags = ceil(kg × (1+waste) ÷ bag) - Concrete calculator — see formula on its page
slab V=l×w×t; footing V=l×w×d; column V=πr²h; wall V=l×h×t; stairs V=n×(tread×riser/2)×w; ramp V=(l×h/2)×w; round V=πr²×t; ring V=π(R²−r²)×h; order = V×(1+waste) - Cement, sand & gravel calculator — see formula on its page
cement = V × kg/m³; aggregates = V × m³/m³; all × (1+waste) - Laminate flooring calculator — see formula on its page
buy_m² = area × (1+waste); boxes = ceil(buy_m² ÷ m²/box) - Baseboard calculator — see formula on its page
net = perimeter − doors; pieces = ceil(net × (1+waste) ÷ piece) - Labour & margin calculator — see formula on its page
markup_sale = cost × (1+m); margin_sale = cost ÷ (1−m) - Full renovation estimator — see formula on its page
total = Σ(area × $/m² per chapter)
Limits
- Quantity estimation, not structural design or site supervision.
- Where professional judgment is required (structure, MEP), the page says so.
- Prices and coverage are indicative unless you use your saved prices.