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Last edited 21 Sep 2026

Converting between weight and volume for bulk construction materials

1 Introduction
2 Bulk density, particle density and specific gravity
3 Loose and compacted volumes
4 The conversion method
5 Worked examples
6 Indicative bulk densities
7 Factors that change bulk density
8 Practical implications for ordering
9 Related articles on Designing Buildings

[edit] Introduction

Bulk construction materials such as aggregate, sand, topsoil and mulch may be supplied and specified by either mass or volume. Suppliers commonly quote the mass of material, particularly where deliveries are weighed, while designers and contractors often calculate requirements by volume from the area and depth of a proposed layer.

Converting between mass and volume is therefore a routine calculation for projects involving loose materials. It can also be a source of over-ordering or under-ordering because the conversion factor is not constant. It depends on the bulk density of the particular material, which varies with its composition, grading, moisture content and degree of compaction.

This article describes the conversion method, distinguishes between different types of density, explains factors that affect bulk density and provides indicative values for materials commonly supplied in bulk.

[edit] Bulk density, particle density and specific gravity

Three different properties can be confused when converting between mass and volume.

Particle density, sometimes referred to as grain density, is the mass of the solid particles divided by the volume of the particles themselves. It excludes the voids between particles. The particle density of common natural mineral aggregates is typically substantially higher than their bulk density.

Bulk density is the mass of a material divided by the total volume it occupies, including the voids between particles. It therefore depends not only on the density of the constituent material but also on particle size distribution, particle shape, moisture content and how the material has been deposited or compacted.

Specific gravity is a dimensionless ratio comparing the density of a material with the density of water. In aggregate testing, relative density is generally determined in relation to the solid particles rather than the bulk volume occupied by a loose aggregate.

Bulk density is the relevant property for converting the mass of a loose material into the volume it occupies. Using particle density instead would produce a substantially different result because the voids between particles would not be accounted for.

[edit] Loose and compacted volumes

A material can occupy different volumes depending on its state. Loose material tipped from a vehicle generally occupies a greater volume than the same material after it has been spread and compacted.

The reduction can be significant for granular sub-base and similar materials. The amount depends on the material, grading, layer thickness, moisture content and compaction method, so a universal compaction allowance should not be assumed.

Where compaction is required, quantities should normally be derived from the compacted design volume and then adjusted using an appropriate allowance based on the material and construction method. Keeping the design volume and compaction allowance as separate quantities makes the calculation easier to check.

[edit] The conversion method

The calculation is straightforward once an appropriate bulk density has been established.

In metric units, where bulk density is expressed in tonnes per cubic metre:

Volume (m³) = mass (tonnes) ÷ bulk density (t/m³)
Mass (tonnes) = volume (m³) × bulk density (t/m³)

For example, a material with a bulk density of 1.60 t/m³ has a volume of 0.625 m³ per tonne.

Equivalent calculations can be made using other units. For US customary units, where bulk density is expressed in short tons per cubic yard:

Volume (yd³) = mass (short tons) ÷ bulk density (short tons/yd³)
Mass (short tons) = volume (yd³) × bulk density (short tons/yd³)

One short ton is 907.18 kg and one cubic yard is approximately 0.7646 m³. A bulk density expressed in short tons per cubic yard can therefore be converted to kilograms per cubic metre by multiplying by approximately 1,186.55. Conversely, 1 tonne per cubic metre is approximately 0.8428 short tons per cubic yard.

The metric tonne, US short ton and imperial long ton are different units. The term ton should therefore be qualified where there is any possibility of ambiguity.

[edit] Worked examples

[edit] Calculating volume from a delivered weight

A 20 tonne delivery of crushed stone has a bulk density of 1.60 t/m³. Its approximate loose volume is:

20 ÷ 1.60 = 12.5 m³

Using US customary units, a 20 short ton load with a bulk density of 1.35 short tons/yd³ would occupy:

20 ÷ 1.35 = 14.8 yd³

These calculations describe the volume corresponding to the stated bulk density. They do not necessarily represent the final compacted volume after the material has been placed.

[edit] Calculating weight from a design volume

A driveway 12 m long and 3 m wide is to receive a 100 mm compacted layer of granular sub-base.

The compacted volume is:

12 × 3 × 0.1 = 3.6 m³

If an allowance of 25% is appropriate for the particular material and compaction process, the estimated loose volume required is:

3.6 × 1.25 = 4.5 m³

At a bulk density of 1.84 t/m³, the corresponding mass is:

4.5 × 1.84 = 8.28 tonnes

This example illustrates why the compacted design volume should not simply be multiplied by a loose bulk density without allowing for the change in volume during compaction.

[edit] Comparing materials with different bulk densities

Ten tonnes of a low-density shredded bark mulch at an indicative bulk density of 0.36 t/m³ would occupy approximately:

10 ÷ 0.36 = 27.8 m³

Ten tonnes of a crushed aggregate with a bulk density of 1.60 t/m³ would occupy approximately:

10 ÷ 1.60 = 6.25 m³

The same mass can therefore represent substantially different delivered volumes depending on the material.

[edit] Indicative bulk densities

The following values are indicative loose bulk densities. They should not be treated as universal values for the named materials. Actual density can vary according to source, grading, particle shape, moisture content, handling and compaction.

Where accurate quantities are required, the density supplied for the particular product should be used. For aggregates, laboratory determination of loose bulk density and voids can be undertaken in accordance with the relevant test standard.

[edit] Crushed stone and gravel

Material	kg/m³	t/m³	m³ per tonne	Short tons/yd³	yd³ per short ton
Crushed stone, 38–63 mm	1,483	1.48	0.67	1.25	0.8
Crushed stone, 19–25 mm	1,602	1.6	0.62	1.35	0.74
Crushed stone, 19 mm	1,602	1.6	0.62	1.35	0.74
Railway ballast rock	1,543	1.54	0.65	1.3	0.77
Gabion stone	1,424	1.42	0.7	1.2	0.83
Pea gravel, 3–10 mm	1,602	1.6	0.62	1.35	0.74
Rip-rap / rock armour	1,483	1.48	0.67	1.25	0.8
Road base / crusher run, 50 mm to fines	1,839	1.84	0.54	1.55	0.65
Stone dust / screenings	1,602	1.6	0.62	1.35	0.74

[edit] Recycled and secondary materials

Material	kg/m³	t/m³	m³ per tonne	Short tons/yd³	yd³ per short ton
Crushed concrete, 19–25 mm	1,424	1.42	0.7	1.2	0.83
Crushed concrete paver base	1,543	1.54	0.65	1.3	0.77
Crushed concrete road base	1,602	1.6	0.62	1.35	0.74
Recycled asphalt planings	1,661	1.66	0.6	1.4	0.71

[edit] Sands

Material	kg/m³	t/m³	m³ per tonne	Short tons/yd³	yd³ per short ton
Concrete sand	1,602	1.6	0.62	1.35	0.74
Building sand	1,543	1.54	0.65	1.3	0.77
Fill sand	1,543	1.54	0.65	1.3	0.77
Beach sand	1,543	1.54	0.65	1.3	0.77
Play sand	1,543	1.54	0.65	1.3	0.77

[edit] Soils

Material	kg/m³	t/m³	m³ per tonne	Short tons/yd³	yd³ per short ton
Topsoil	1,305	1.31	0.77	1.1	0.91
Subsoil fill	1,483	1.48	0.67	1.25	0.8
Red clay	1,543	1.54	0.65	1.3	0.77
Sports-surface clay	1,543	1.54	0.65	1.3	0.77
Garden soil mix	1,009	1.01	0.99	0.85	1.18
Compost	712	0.71	1.4	0.6	1.67

[edit] Mulches and wood products

Material	kg/m³	t/m³	m³ per tonne	Short tons/yd³	yd³ per short ton
Shredded bark mulch	356	0.36	2.81	0.3	3.33
Engineered wood fibre	356	0.36	2.81	0.3	3.33
Pine bark nuggets	261	0.26	3.83	0.22	4.55

[edit] Factors that change bulk density

Moisture content affects bulk density because water adds mass and can also alter the arrangement of particles. A wet material may therefore have a greater mass per unit volume than the same material in a dry condition. The effect can be particularly significant for sands and organic materials such as compost and bark.

Compaction and handling also affect bulk density. Material that has been stockpiled, vibrated during transport or placed and compacted in layers may have a higher density than freshly tipped loose material. The density measured when material is loaded is therefore not necessarily the same as the density after delivery and placement.

Grading has a significant effect because smaller particles can occupy some of the voids between larger particles. A well-graded aggregate can therefore have a higher bulk density than a single-sized aggregate of similar mineral composition. Materials containing a wide range of particle sizes, such as crusher-run or road-base materials, can consequently have different bulk densities from single-sized decorative aggregates.

Particle shape and angularity also affect packing. Angular crushed rock can have a different loose void ratio from rounded aggregate, while the difference can change after compaction.

The source material is another factor. Aggregates produced from different rocks can have different particle densities, porosities and bulk densities even when their grading is similar. Recycled aggregates can also differ from primary aggregates because of variations in adhered mortar, ceramics, asphalt and other constituent materials.

[edit] Practical implications for ordering

The first step is to establish whether the quantity is being specified by mass or volume and whether the stated density is loose or compacted. The unit system should also be confirmed, particularly where tonnes, short tons or long tons could be confused.

Where possible, the bulk density of the specific product should be obtained rather than relying on a generic value. This is particularly important for recycled, blended and organic materials, where variation can be significant.

For materials that will be compacted, the quantity should be based on the finished compacted volume with a separate allowance for the expected change in volume during placement and compaction. The assumptions used should be recorded so that the quantity can be checked against the construction method.

The volume of a delivery should also be considered alongside its mass. Although material may be priced by weight, the volume affects storage requirements, the number of deliveries and the practical logistics of handling and placing the material.