Material densities and assumptions

Every number the calculators depend on, with its range, its source and when it was last checked. This table is generated from the same data the engine uses, so it cannot fall out of step with the calculators.

Last reviewed 2026-07-01.

Note: Densities are ranges, not constants

Bulk density varies with moisture, grading, compaction and the quarry it came from. The figures below are typical loose bulk densities as delivered. Where a range is given, wet or well-graded material sits at the top of it. If your supplier quotes a density for the material they are actually selling you, use theirs.

Densities

Bulk densities used by the calculators, with ranges and sources
Material	Value	Range	Region	Source
20 mm gravel / ¾ in gravelLoose bulk density as delivered, not compacted.	1,600 kg/m³	1,500–1,700	Both	Typical loose bulk densities for construction aggregatesMineral Products Association
Pea gravel / pea shingleRounded 10 mm material. Migrates underfoot, so it is a poor choice for driveways.	1,600 kg/m³	1,500–1,700	Both	Typical loose bulk densities for construction aggregatesMineral Products Association
Crushed stone / angular chippingsAngular material interlocks, so it holds a driveway surface better than pea gravel.	1,600 kg/m³	1,500–1,750	Both	Typical loose bulk densities for construction aggregatesMineral Products Association
Limestone chippingsLighter than granite. Dusts down over time and beds in.	1,550 kg/m³	1,500–1,650	Both	Typical loose bulk densities for construction aggregatesMineral Products Association
MOT Type 1 sub-baseGraded crushed rock to the Series 800 specification.	2,000 kg/m³	1,900–2,100	UK	Manual of Contract Documents for Highway Works, Series 800: Road Pavements — UnboundNational Highways (UK)
Crushed aggregate base / road baseDense-graded base material, the US equivalent of MOT Type 1.	2,100 kg/m³	1,950–2,200	US	Typical loose bulk densities for construction aggregatesMineral Products Association
Slate chippingsPlate-shaped and noticeably lighter per cubic metre than rounded gravel.	1,300 kg/m³	1,250–1,400	Both	Typical loose bulk densities for construction aggregatesMineral Products Association
Decorative stoneCovers cobbles, spar and mixed decorative grades. Check the bag for a stated density.	1,500 kg/m³	1,400–1,650	Both	Typical loose bulk densities for construction aggregatesMineral Products Association
Sharp sand / concrete sandDamp sand bulks up in volume but the delivered weight is what you pay for.	1,600 kg/m³	1,500–1,700	Both	Typical loose bulk densities for construction aggregatesMineral Products Association
Building sand / mason sandSoft sand used for bricklaying mortar.	1,500 kg/m³	1,400–1,600	Both	Typical loose bulk densities for construction aggregatesMineral Products Association
Screened topsoilScreened, moist topsoil. Very wet soil can exceed 1,500 kg/m³.	1,300 kg/m³	1,100–1,500	Both	BS 3882: Specification for topsoilBritish Standards Institution
Wet concreteNormal-weight concrete. Lightweight mixes are considerably lighter.	2,400 kg/m³	2,300–2,500	Both	BS 8500: Concrete — Complementary British Standard to BS EN 206British Standards Institution
Wet mortarCement:sand mortar, mixed and placed.	2,100 kg/m³	2,000–2,200	Both	BS EN 998-2: Specification for mortar for masonry — Masonry mortarBritish Standards Institution
Cement powder (loose)Used to convert a mortar mix ratio into bags of cement.	1,440 kg/m³	—	Both	Typical loose bulk densities for construction aggregatesMineral Products Association
Treated softwood decking and framingFreshly treated timber is heavier than kiln-dried stock and can exceed the range.	550 kg/m³	450–650	Both	Characteristic densities for C16/C24 European softwoodTRADA / BS EN 338
Composite decking boardSolid-profile figure. Hollow-core composite boards weigh roughly 40% less.	1,150 kg/m³	950–1,350	Both	Typical loose bulk densities for construction aggregatesMineral Products Association

Yields, coverage and allowances

Bag yields, coverage rates, compaction factors and default allowances
Assumption	Value	Notes	Source
UK standard brick co-ordinating size	60 bricks/m² per half-brick skin59–61	215 × 102.5 × 65 mm brick plus 10 mm joints gives a 225 × 75 mm face module. 1 ÷ (0.225 × 0.075) = 59.26, universally quoted and specified as 60 per m².	Brick Development AssociationReviewed 2026-07-01
US modular brick coursing	6.86 bricks/ft² per wythe	Modular brick 7⅝ × 3⅝ × 2¼ in with ⅜ in joints gives an 8 × 2⅔ in face module. The 6.86 per square foot figure is the industry-standard estimating rate.	Brick Industry AssociationReviewed 2026-07-01
UK concrete block coursing	10 blocks/m²	440 × 215 mm block plus 10 mm joints gives a 450 × 225 mm module: 9.88 per m².	Project EstimateReviewed 2026-07-01
US concrete masonry unit coursing	1.125 blocks/ft²	Nominal 8 × 16 in face including joints: 1 ÷ (16/12 × 8/12) = 1.125 per ft².	National Concrete Masonry AssociationReviewed 2026-07-01
Bagged ready-to-use concrete yield	0 m³ per kg of dry mix0–0.001	Derived from the published 80 lb (36.3 kg) ≈ 0.60 ft³ (0.0170 m³) yield. UK 20 kg and 25 kg bag yields are calculated from the same rate: 0.0094 m³ and 0.0118 m³.	Bagged concrete manufacturers (Quikrete, Sakrete)Reviewed 2026-07-01
Mortar volume per m² of half-brick UK brickwork	0.033 m³/m²0.025–0.04	Bed and perp joints alone are 0.0176 m³/m². Filling the frog adds a further 0.0089 m³/m², and a 1.25× site allowance covers over-filling, droppings and mixer residue. That gives roughly 0.55 m³ of mortar — about 0.9 tonnes of sand — per 1,000 bricks, which matches the trade rule of about a tonne of sand per thousand. Solid bricks with no frog, and blockwork, need considerably less.	Project EstimateReviewed 2026-07-01
Sand required per m³ of 1:5 mortar	1.6 tonnes/m³1.5–1.7	Allows for bulking; damp sand delivered by weight is the practical ordering unit.	British Standards InstitutionReviewed 2026-07-01
Default waste allowance	10 %5–15	Covers cutting, breakage, setting-out error and the odd unusable unit. Simple rectangles justify 5%; cut-heavy or patterned work justifies 15% or more.	Project EstimateReviewed 2026-07-01
Compaction allowance for granular sub-base	1.3 × loose volume1.2–1.4	Order about 30% more loose material than the finished compacted depth. Whacker-plate compaction on a domestic patio sits near the bottom of the range; roller compaction near the top.	National Highways (UK)Reviewed 2026-07-01
Topsoil settlement allowance	20 %10–25	Freshly tipped soil settles as it is watered and worked. Raised beds settle most. Ignoring settlement is the single most common reason a topsoil order comes up short.	British Standards InstitutionReviewed 2026-07-01
Wall ties for cavity masonry	2.5 ties/m²	900 mm horizontal × 450 mm vertical spacing gives 2.47 per m², specified as 2.5. Extra ties are required at openings and movement joints — typically one every 300 mm vertically.	British Standards InstitutionReviewed 2026-07-01
Deck joist spacing	400 mm centres300–600	400 mm (16 in) centres suit most 32–38 mm softwood boards laid square to the joists. Composite boards commonly require 300–400 mm, and 300 mm or less for diagonal laying. Follow the board manufacturer's span table.	Timber Decking and Cladding AssociationReviewed 2026-07-01

How these are maintained

Each assumption has an id, a value, an optional range, a source, a review date and notes. They live in the codebase next to the calculators, and a change to any of them has to pass the calculation test suite before it can be deployed.

Assumptions marked derivedare calculated from geometry or from another cited figure rather than quoted from a document. Brick coverage is derived from the standard co-ordinating size, for instance, rather than taken from a merchant’s website — that way a non-standard joint width still produces the right answer.

If a figure disagrees with what your supplier tells you, report it. Reports are checked against the published source and a genuine discrepancy is treated as a bug.