Every number has a method.

Transparent arithmetic

Flooring and tile: measured area = length × width. Planned need = area × (1 + allowance/100). Identical products are grouped before purchased packs = ceiling(total planned need / pack coverage). This is an area estimate, not a cut optimiser or an installation layout.

Paint: wall area = 2 × (length + width) × height − openings. Add the ceiling only if it uses the same paint. Litres or US gallons = surface × coats × (1 + allowance/100) / single-coat coverage. Round to whole tins after pooling compatible products.

Grouping rules

Combining is opt-in on every row and off by default. Blank product names are rejected. Product name is case-sensitive. Material kind, units, pack size, pack price and paint coverage must also match. Different colours, batches or finishes must have different product names. Rows in different unit systems are not automatically pooled. Convert them to matching units and check the values first.

Precision and conversions

One foot is exactly 0.3048 metres; one US gallon is 3.785411784 litres. Calculations retain numeric precision internally and only round display values. A small machine-precision tolerance prevents accidental extra packs at an exact integer boundary. Currency labels do not convert prices.

Worked checks

Two 9 m² rooms, 10% allowance and 3 m² packs: need 19.8 m², buy 7 packs. A 4 × 3 × 2.4 m room, 2 m² openings, 2 coats, 10% allowance and 10 m²/L: need 6.952 L, buy 3 tins of 2.5 L.

Limits and review

This release supports rectangular rooms, area-based floor/tile estimates, 40 material rows and 300 KB JSON backups. No structural, electrical, load-bearing, hazardous-material or tax advice is provided. Irregular paint geometry, separate trim/primer estimates, arbitrary polygon plans and cut layouts are not supported. Validate measurements and material suitability with a competent supplier or installer.

Methodology reviewed September 14, 2026. Automated arithmetic and structural tests accompany the source package. That is not a claim of professional certification, browser audit completion or WCAG conformance.

Further reference

Inch Calculator: flooring calculation and installation considerations; Sherwin-Williams: paint calculator and supplier verification. Product-specific instructions take precedence over generic examples.