Construction & DIY Reference
The numbers our DIY calculators apply: area and volume formulas, typical coverage rates, standard waste allowances and the conversion factors that trip people up between a tape measure and a product label. Each card links to the calculator that uses it.
Areas & volumes
Every quantity question on a building job is one of these three shapes. Get the shape right and the rest is division.
Slab volume
cubic metres- L, W — length and width in metres
- D — depth in metres — 100 mm is 0.1, not 100
- Multiple pours — multiply by the number of identical slabs
Depth in the wrong unit is the single most common estimating error: 100 mm entered as 100 overstates a pour a thousandfold.
Open the Concrete Calculator →Wall area of a room
square metres- H — wall height, floor to ceiling
- Standard door — 1.9 m² deducted
- Standard window — 1.4 m² deducted
- Ceiling — add L × W if painting it
Deduct doors and large windows; do not deduct anything small — the offcut is rarely reusable.
Open the Paint Calculator →Tiles per square metre
tiles- w, h — tile width and height in metres
- 300 × 600 mm — 5.56 tiles per m²
- 200 × 200 mm — 25 tiles per m²
- 600 × 600 mm — 2.78 tiles per m²
Work in whole tiles and whole boxes — a part box is not a purchasable unit.
Open the Tile Calculator →Coverage & pack sizes
What one unit of product actually covers. These are typical figures; the label on the tin or pack overrides them every time.
Paint coverage
m² per litre- Typical emulsion — 10–14 m² per litre per coat
- Fresh plaster — absorbs far more on the first coat
- Coats — two is standard; three over a colour change
- Litres needed — area × coats ÷ coverage
Coverage is quoted per coat. Halving it because you are doing two coats double-counts.
Open the Paint Calculator →Flooring pack
m² per pack- Laminate and vinyl planks — typically 1.8–2.5 m² per pack
- Packs needed — area with waste ÷ pack area, rounded up
- Spare — what the rounding up leaves you
Keep the spare rather than returning it — a later batch will not match the shade.
Open the Flooring Calculator →Tile box
tiles per box- Boxes needed — tiles with waste ÷ tiles per box, rounded up
- Adhesive — check the bag: coverage depends on bed depth
- Grout — depends on joint width and tile depth
Box counts differ by range even within one manufacturer — read the box, do not assume.
Open the Tile Calculator →Waste allowances
Waste is not padding. It is the material that ends up as offcuts, breakages and absorption, and leaving it out is why jobs stop halfway.
Standard allowance
of the measured quantity- Simple rectangular room — 10%
- Straight-lay flooring or tiling — 10%
- Concrete — 10% covers spillage and an uneven sub-base
The default on every calculator in this cluster, and the right figure for most jobs.
Open the Concrete Calculator →When to use 15%
of the measured quantity- Diagonal tile layouts — more edge cuts
- Herringbone or chevron flooring — substantially more
- Rooms with many fittings — cuts around each one
- Patterned tile needing alignment — wastage rises with repeat size
Any layout that is not parallel to the walls generates more offcuts than a straight lay.
Open the Tile Calculator →Why running short costs more
consequence- Second delivery — another charge, another wait
- Batch variation — tiles, paint and boards vary between batches
- Labour — a trade back for a second visit
Over-ordering by 10% is cheaper than a second delivery in nearly every case.
Weights & conversions
Products are sold in metric or imperial depending on where you are. Convert first, then calculate — never round as you go.
Concrete density
kg per m³- 1 m³ — ≈ 2,400 kg (2.4 tonnes)
- 0.5 m³ — ≈ 1,200 kg
- Reinforced — slightly higher, ~2,500 kg/m³
Used to convert a volume into a delivery weight. Bagged yields differ by product — read the bag.
Open the Concrete Calculator →Length & area factors
exact- 1 inch — 0.0254 m (exact)
- 1 m² — 10.7639 ft²
- 1 m³ — 1.30795 yd³
- 1 yd³ — 0.7646 m³
The foot and inch factors are exact by definition, not approximations.
Open the Concrete Calculator →Measuring the space
method- Each wall — measure at floor level and at head height
- Use — the larger of the two figures
- Never — trust a drawing over a tape measure
Rooms are rarely square and plans are rarely current.
Key figures at a glance
How to use this page
Read a figure here when you want to know why a calculator produced what it produced, or when you are standing in a merchant with a product label in your hand. Each card gives the whole rule rather than one worked answer, so it works as a lookup as well as an explanation. If you want the arithmetic done, follow the link at the foot of the card.
What these figures do not cover
These are quantity estimates. Nothing on this page tells you what concrete mix a job needs, whether a floor can carry a load, what primer a surface wants, or how a substrate should be prepared. Those are specification questions governed by standards and by the manufacturer's data sheet, and structural questions need a qualified engineer. Coverage rates in particular are typical values: absorbency, application method and surface texture move them significantly.
Sources & references
Every figure on this page traces to one of these. Where the governing document is a paywalled standard we name it rather than link a shop front:
- BS 8500-1 and BS 8500-2 — the British Standard for specifying and producing concrete — the authority on mix specification, which these volume tools deliberately do not attempt
- BS 5385-1 — wall and floor tiling: design and installation of ceramic tiling, including substrate and movement-joint requirements
- BS 8203 — installation of resilient floorcoverings — subfloor preparation and acclimatisation, neither of which a quantity calculator can assess
- The product data sheet — the only authority on the coverage rate, bag yield, pack area and box count of the specific product you are buying
Further reading
Where the waste actually goes, and why rounding up to whole boxes and packs usually moves an order further than the percentage you chose.
Cite this page
You are welcome to quote these figures in a lesson, a forum answer, a wiki or a write-up. A link back is all we ask — it lets your reader check the figure against its source, which is the point of the page.
Tool Corner, “Construction & DIY Reference”. Updated 29 July 2026. https://toolcorner.net/construction-reference.html
Every figure is dated, and the sources above are linked wherever a stable public page exists, so a citation here can be traced rather than taken on trust.