Methodology

Last updated 2026-10-18

Principles

Pure, tested formulas. Calculations run in your browser as small, deterministic functions. Each calculator has golden test cases computed by hand, run on every build.
SI internally. Inputs are converted to metres, square metres and cubic metres, calculated, then converted back for display. This avoids mixing units mid-calculation.
Round up to buy. Bags, boxes, sheets, bundles and tins are rounded up to whole units (with a tiny tolerance so 45.0000001 bags becomes 45, not 46).
Defaults are editable. Bag yields, coverage rates and densities are typical label or industry values. Every one can be changed under Advanced options.

Conversion constants

Exact or standard factors used (NIST SP 811)
Quantity	Value
1 foot	0.3048 m (exact)
1 inch	0.0254 m (exact)
1 cubic yard	27 cu ft = 0.764555 m³
1 US gallon	3.785411784 L (exact)
1 pound	0.45359237 kg (exact)
1 short ton	2,000 lb = 907.18 kg
1 roofing square	100 sq ft = 9.29 m²

Waste factors

Waste allowances cover offcuts, breakage, spillage and uneven surfaces. They are presented as typical ranges from manufacturer and installer guidance, not as a standard. Our defaults sit in the middle of the usual range; pattern-dependent defaults (tile, flooring, roofing) change automatically with the layout you choose.

Calculators and formulas

Concrete Slab Calculator — Volume (cu ft) = Length (ft) × Width (ft) × Thickness (in) ÷ 12
Concrete Bag Calculator — Bags = Volume × (1 + waste %) ÷ yield per bag, rounded up
Paint Calculator — Wall area = 2 × (Length + Width) × Height − openings
Tile Calculator — Tiles = Area ÷ ((Tile length + joint) × (Tile width + joint))
Flooring Calculator — Area = Length × Width (+ extra rectangles)
Square Footage Calculator — Rectangle: Length × Width
Mulch Calculator — Volume (cu ft) = Area (sq ft) × Depth (in) ÷ 12
Gravel Calculator — Volume = Length × Width × Depth × (1 + waste %)
Drywall Calculator — Walls = 2 × (Length + Width) × Height − openings
Roofing (Shingle) Calculator — Pitch factor = √(1 + (Rise ÷ 12)²)
Deck Board Calculator — Rows = Deck width ÷ (Board width + Gap), rounded up
Fence Calculator — Sections = (Fence length − Gate widths) ÷ Post spacing, rounded up
Topsoil Calculator — Volume = Length × Width × Depth × (1 + settling %)
Paver Calculator — Pavers = Area ÷ ((Paver L + Joint) × (Paver W + Joint)) × (1 + waste %)
Brick Calculator — Bricks per area = 1 ÷ ((Brick L + Joint) × (Brick H + Joint))
Board Foot Calculator — Board feet = Thickness (in) × Width (in) × Length (ft) ÷ 12 × Pieces
Stair Calculator — Risers = Total rise ÷ Max riser, rounded up
Wallpaper Calculator — Drops = (Perimeter − ½ openings) ÷ Roll width, rounded up
Cubic Yard Calculator — Cubic feet = Length (ft) × Width (ft) × Depth (in) ÷ 12
Feet and Inches Calculator — Inches = Feet × 12 + Inches + Numerator ÷ Denominator

What we don't do

We don't provide structural design, electrical or plumbing compliance calculations. Where loads, spans or safety are involved, consult local codes and a licensed professional.

Change log

2026-10-18 · v0.2.0 — Added 10 calculators (deck boards, fence, topsoil, pavers, bricks, board feet, stairs, wallpaper, cubic yards, feet & inches) and the Decking, Fencing, Framing & Lumber and Masonry hubs; published 12 guides; expanded every calculator page with in-depth planning notes; stair pitch is now measured along the nosing line (riser ÷ tread); unit labels now follow the selected unit system.
2026-10-17 · v0.1.0 — First release of 10 calculators.