What this field is for
The Volume of declared unit field asks for the physical volume, in m³, that one declared unit (DU) of your product takes up. The software uses this value together with the mass of the declared unit to calculate the product's gross density, which is published in digital EPD formats.
Gross density (kg/m³) = mass of the declared unit (kg) ÷ volume of the declared unit (m³) |
The kind of volume you enter matters. Designers use digital EPDs in BIM and building-level tools, which work out a product's mass from the volume of the object drawn in the model. A BIM model draws a product's outer shape: a pipe as a solid cylinder, an inverter as a box. So the volume you enter needs to be measured the same way, as the space enclosed by the product's outer surface, including any cavities, air or voids inside it. This is called the external envelope volume.
Only enter the volume of the product itself. Leave out packaging and transport volume, unless your declared unit explicitly includes packaging. If you're unsure what your declared unit is, see Functional and Declared Units.
How to work out the volume
You usually won't have a volume figure ready to copy, so you'll calculate it from the product's dimensions. It often helps to start from whatever quantity is easiest to measure and scale up or down to the declared unit afterwards.
Choose a reference quantity. This can be the declared unit itself, or something easier to measure, such as one piece, 1 m² or 1 m of product.
Measure its outer volume as installed. Use the external dimensions, or the CAD body for irregular shapes. Keep any internal cavities in the volume rather than subtracting them.
Scale to one declared unit. If your declared unit is a mass, such as 1 kg or 1 t, divide the declared unit's mass by the mass of your reference, then multiply by the reference volume.
Enter the result in m³. If your dimensions are in millimetres, divide each by 1,000 before multiplying them together.
For products declared per area, there's a shortcut: the volume of 1 m² is simply the installed thickness in metres. A 100 mm board, for example, has a volume of 0.100 m³ per m².
Which volume to use for your product
The formula never changes, but how you measure the outer volume depends on the shape of the product. Find your product type below.
Product type | Examples | Volume to enter |
Homogeneous solid | Concrete, timber, solid boards | External dimensions |
Layered | Sandwich panels, insulated boards, laminates | Area × total installed thickness |
Profiled / ribbed | Trapezoidal roof panels, profiled sheets | Area × overall depth including the ribs (as drawn in BIM) |
Hollow sections | Pipes, hollow blocks, ducts | Outer cross-section × length, cavity included |
Assembled / electronic | Inverters, luminaires, HVAC units | Bounding box of the casing, or the CAD outer volume |
Irregular | Fittings, fixings, castings | CAD outer volume (a bounding box only if the product is modelled as a box in BIM) |
Granular / loose | Aggregates, sand | Volume as placed; state whether loose or compacted |
Product ranges (average EPD) | Several sizes in one EPD | Weighted average volume of the products |
For profiled, irregular, granular and averaged products there is more than one reasonable way to measure, so note in the EPD which convention you used. This lets the verifier reproduce your value.
Example: an inverter
Assembled products like inverters are where mistakes happen most often, so here is one worked through step by step. The declared unit is 1 piece. One inverter weighs 25 kg without packaging, and its casing measures 600 × 400 × 200 mm.
First, convert the casing dimensions to metres: 0.60 m × 0.40 m × 0.20 m. The inverter is modelled in BIM as a box of this size, so its bounding box is the right volume.
Volume of declared unit = 0.60 × 0.40 × 0.20 = 0.048 m³
Enter 0.048 in the field. The software then calculates:
Gross density = 25 kg ÷ 0.048 m³ = 520 kg/m³
It can be tempting to add up the volumes of the materials inside instead: 12 kg of aluminium, 5 kg of steel, 3 kg of copper, 3 kg of plastics and 2 kg of electronics. That gives only around 0.009 m³, because it leaves out all the air inside the casing. The resulting density would be about 2,780 kg/m³, more than five times too high, and any BIM tool using it would overstate the inverter's mass in the same way.
More examples
The table below shows the same approach for other product types. The last column is the gross density the software will calculate, so you can use it to sanity-check your own result.
Product | Declared unit | How the volume is worked out | Enter (m³) | Resulting density (kg/m³) |
Ready-mixed concrete C30/37 | 1 m³ | The declared unit is already a volume | 1 | 2,400 |
Glulam, 12% moisture | 1 m³ | The declared unit is already a volume; state the moisture content | 1 | 470 |
Steel–EPS sandwich panel, 100 mm, 10 kg/m² | 10 kg | 10 kg = 1 m² of panel → 1 m² × 0.100 m | 0.100 | 100 |
Trapezoidal roof panel, 135 mm overall depth (100 mm core) | 1 m² | 1 m² × 0.135 m overall depth. Using the 0.100 m core would overstate density by ~35% | 0.135 | 89 |
Inverter, 25 kg | 1 piece | Casing 0.60 × 0.40 × 0.20 m | 0.048 | 520 |
Steel pipe, Ø 60.3 mm, 5.03 kg/m | 1 m | π/4 × 0.0603² × 1 m, bore included | 0.00286 | 1,760 |
Cast steel bracket, 1.2 kg | 1 piece | CAD body volume of the closed outer surface | 0.000153 | 7,840 |
Crushed aggregate 0/32, loose | 1 t | 1,000 kg ÷ 1,550 kg/m³ loose bulk density as delivered | 0.65 | 1,550 |
Inverter range (30% small, 50% medium, 20% large) | 1 piece, average | 0.3 × 0.040 + 0.5 × 0.048 + 0.2 × 0.070 | 0.050 | 530 (range 500–570) |
A few of these are worth a closer look:
Steel pipe: the bore counts as part of the volume, which is why the result (1,760 kg/m³) is well below the density of steel itself (7,850 kg/m³). Gaps between stacked pipes don't count, as they aren't part of a single product.
Cast steel bracket: a bounding box (0.15 × 0.10 × 0.10 m = 0.0015 m³) is only acceptable if the bracket is modelled as a box in BIM, and you should say so in the EPD.
Aggregate: for granular products, the gaps between grains are part of the product as placed. Compacted aggregate would be around 2,100 kg/m³, so state which one you used.
Product range: average the volumes (and masses) by production share, never the densities. Also declare the range, so users of a specific size can pick the right value.
Common mistakes
Mistake | What to do instead |
Entering the solid material volume (from a bill of materials or datasheet densities) | Use the outer envelope volume |
Subtracting cavities, bores or the air inside casings and foams | Keep them in the volume |
Including packaging or pallet volume | Product only, unless the declared unit includes packaging |
Using the volume of a stacked load or container | Use a single product's envelope |
Using core thickness for profiled panels | Use the overall depth including ribs |
Entering mm³ or litres | Convert to m³ (1 litre = 0.001 m³) |
Before you submit
Before saving, it's worth a quick check: divide the declared unit's mass by the volume you entered, and look at the result.
The result should not exceed the density of the product's solid material. If it does, the volume is too small.
It should be close to the material density for solid products, and well below it for hollow, foamed or assembled ones.
It should match the dimensions and mass conversion factor stated in the EPD.
What to ask the manufacturer/supplier for
If you're collecting data from a manufacturer or supplier, ask for dimensions rather than a density. Datasheet densities usually describe the solid material, not the product as installed, so it's safer to work out the volume yourself. The inputs you need are:
External dimensions as installed: length × width × height, thickness, or outer diameter
Product mass per piece, m² or m, without packaging
The CAD outer volume, if the shape is irregular
For profiled products, both the overall depth and the core thickness
If you have any questions about the volume for your own product, please reach out to us via the support widget in the software.