Two parcels. One holds four hardback books and weighs 3.4kg. The other holds a winter duvet and weighs 3.0kg. The lighter one costs several times more to send.
That is not a pricing error. It is volumetric weight, and it is the single most useful concept to understand if you want to control what you spend on delivery.
What volumetric weight is
A courier's real constraint is not weight, it is space. A van has a fixed load volume, and it fills up with bulky items long before it reaches its weight limit. If pricing were purely by weight, a van full of duvets would generate almost no revenue while taking a driver all day.
So couriers convert a parcel's volume into a weight equivalent — its volumetric weight, sometimes called dimensional or cubic weight — and charge on whichever is greater: actual or volumetric.
Chargeable weight = the greater of actual weight and volumetric weight
The calculation
Measure the sealed parcel in centimetres, then:
(Length × Width × Height) ÷ 5000 = volumetric weight in kg
For a 40 × 30 × 20cm parcel: 40 × 30 × 20 = 24,000 cm³. Divided by 5000, that is 4.8kg. If the parcel actually weighs 2kg, you pay the 4.8kg rate. If it weighs 7kg, you pay the 7kg rate.
Always measure the finished, sealed parcel at its widest points, including any bulge in the packaging. The courier measures what arrives at the depot — a box that bows outwards measures larger than the flat-pack dimensions printed on it.
About the divisor
5000 is the standard divisor for UK road services and the figure we use. You will see others:
| Divisor | Typically used for | Effect |
|---|---|---|
| 6000 | Some air freight | Lowest volumetric weight |
| 5000 | UK and European road | Standard |
| 4000 | Some express air services | Higher volumetric weight |
| 3000 | Certain premium express | Highest volumetric weight |
A lower divisor means a higher volumetric weight for the same box, so when comparing carriers, compare divisors as well as headline rates. A cheaper rate calculated on a 4000 divisor can easily cost more than a higher rate on 5000.
Worked examples
| Parcel | Dimensions | Volume | Volumetric | Actual | Charged on |
|---|---|---|---|---|---|
| Books ×4 | 30 × 24 × 12cm | 8,640 cm³ | 1.7kg | 3.4kg | 3.4kg actual |
| Trainers | 34 × 22 × 13cm | 9,724 cm³ | 1.9kg | 1.2kg | 1.9kg volumetric |
| Winter duvet | 60 × 45 × 40cm | 108,000 cm³ | 21.6kg | 3.0kg | 21.6kg volumetric |
| Duvet, vacuum-packed | 40 × 30 × 25cm | 30,000 cm³ | 6.0kg | 3.1kg | 6.0kg volumetric |
| Lampshade | 45 × 45 × 45cm | 91,125 cm³ | 18.2kg | 0.9kg | 18.2kg volumetric |
Rows three and four are the same duvet. Vacuum-packing it and dropping to a smaller box takes chargeable weight from 21.6kg to 6kg — a reduction of roughly 72% for about two minutes of work.
Which items are usually priced on volume
Anything with a low density. As a rule of thumb, if a parcel feels lighter than it looks, it is probably being charged volumetrically:
- Duvets, pillows, cushions, blankets
- Lampshades and light fittings
- Empty containers, vases, plant pots
- Crisps, cereal, confectionery and other packaged snacks
- Soft toys
- Bulky clothing — coats, knitwear
- Anything in polystyrene protective packaging
- Assembled furniture parts and garden items
Conversely, books, tools, tiles, liquids, metal parts and machinery are dense and almost always charged on actual weight.
Cutting volumetric weight
The maths rewards small reductions disproportionately, because you are working in three dimensions. Take 5cm off each side of a 40 × 30 × 25cm box and the volumetric weight falls from 6kg to 3.9kg — a 35% cut from what looks like a minor change.
- Use the smallest box that still allows about 5cm of padding. Both goals matter; a crushed parcel is not a saving.
- Compress soft goods. Vacuum bags for bedding and bulky clothing are the highest-return trick available.
- Use mailing bags where protection allows. Bags conform to the contents and have almost no volumetric penalty.
- Do not ship air. A half-empty box padded out with void fill is paying for the void fill's volume.
- Disassemble where sensible. Removing legs from a small table can halve the box.
- Stock several box sizes. Two sizes guarantees most orders travel in a box that is too big — see cutting shipping costs.
- Watch for bulge. An overfilled box measures larger than its nominal size.
Under-declaring dimensions to get a cheaper quote does not work: parcels are measured at the depot and re-graded, which means an adjustment charge and a handling delay. Declare the parcel accurately and reduce the actual box instead.
Girth and length limits
Separately from volumetric weight, most parcel services cap physical dimensions — commonly around 120cm on the longest side, with a limit on length plus girth. Exceed them and the parcel moves onto a freight rate rather than simply costing a bit more, because it no longer fits the automated sorting equipment.
If you regularly ship long items such as rolled artwork, curtain poles or skirting board, check the limits before you build the packaging.
A quick reference
| Box size (cm) | Volumetric weight (÷5000) |
|---|---|
| 20 × 15 × 10 | 0.6kg |
| 30 × 20 × 15 | 1.8kg |
| 35 × 25 × 20 | 3.5kg |
| 40 × 30 × 25 | 6.0kg |
| 50 × 40 × 30 | 12.0kg |
| 60 × 40 × 40 | 19.2kg |
| 60 × 50 × 50 | 30.0kg |
Keep this near your packing bench. Knowing that a 60 × 40 × 40cm box starts at 19.2kg regardless of contents changes how you choose boxes.
Frequently asked questions
The most common questions about parcel measurement are below, with more on pricing in our guide to what it costs to send a parcel in the UK.
Check a real parcel
Measure and weigh your parcel, then put both figures into the Fleet Express quote tool. It applies the calculation for you and shows the price across every service, so you can see immediately whether a smaller box would pay for itself.
