Cubic weight is a weight worked out from an item’s size, not from what it weighs on the scales. Carriers compare it with the actual weight and charge whichever is higher, so a big, light box can cost more than a small, heavy one. Here’s how to calculate cubic weight, which conversion factors are common in Australia and how to cut your freight costs.
Dead weight vs cubic weight
Dead weight is the actual weight of your item, read off a scale. Cubic weight, also called volumetric or dimensional weight, turns the space your item takes up into a weight.
Space matters because a van, truck or aircraft fills up by volume as well as by weight. A load of pillows weighs very little but can still fill a whole van. If carriers charged on dead weight alone, bulky, light freight would travel for almost nothing.
So most carriers work out both figures and charge on the higher one, often called the chargeable weight. Australia Post, for example, typically charges the greater of cubic or actual weight for parcels in your own packaging.
How to calculate cubic weight
The formula is length × width × height in metres, multiplied by the carrier’s conversion factor. The factor is expressed in kilograms per cubic metre (kg/m³).
- Measure the length, width and height of the packed item at its longest points.
- Convert each measurement to metres. For example, 45 cm becomes 0.45 m.
- Multiply the three figures together to get the volume in cubic metres.
- Multiply the volume by the conversion factor, such as 250.
- Compare the result with the dead weight. The higher number is the one you pay on.
Say a carton measures 0.5 m × 0.4 m × 0.4 m. Its volume is 0.08 m³, so at a factor of 250 its cubic weight is 20 kg. If it weighs 8 kg on the scales, it’s charged as 20 kg.
Measuring tips
- Measure the outside of the packaging, not the product inside.
- Include handles, lids and bulges that stick out.
- For tubes, cylinders and odd shapes, use the maximum point for each dimension.
- Measure pallets from the floor to the top of the load, including the pallet base and any overhang.
Cubic weight conversion factors commonly used in Australia
Each carrier sets its own conversion factor, and it can differ between services. These are the figures you’ll see most often.
- Domestic parcels and road express: 250 kg/m³. Australia Post uses 250, and TNT’s Australian site lists 250 for its domestic express services. That’s the same as dividing cubic centimetres by 4,000.
- International air freight: about 167 kg/m³. IATA describes the general rule as dividing the volume in cubic centimetres by 6,000.
- International express couriers: often 200 kg/m³. TNT, for example, lists 200 for its international express services, the same as dividing cubic centimetres by 5,000.
A higher factor gives a higher cubic weight for the same box. That’s why one carton can have a different chargeable weight by road and by air. Pallet pricing also varies between carriers. Check the factor on your rate card, or ask your carrier how your freight will be charged.
Worked example: three shipments compared
The table uses 250 kg/m³, a common factor for domestic parcels and road freight. The pallet uses the standard Australian footprint of 1165 × 1165 mm, with stock stacked to 1.2 m including the base.
| Shipment | Size (L × W × H) | Volume | Dead weight | Cubic weight | Charged on |
|---|---|---|---|---|---|
| Light, bulky carton (cushions) | 0.60 × 0.50 × 0.50 m | 0.15 m³ | 4 kg | 37.5 kg | 37.5 kg (cubic) |
| Small, dense carton (bolts) | 0.30 × 0.25 × 0.20 m | 0.015 m³ | 12 kg | 3.75 kg | 12 kg (dead) |
| Pallet of boxed stock | 1.165 × 1.165 × 1.20 m | 1.63 m³ | 300 kg | 407 kg | 407 kg (cubic) |
The bulky carton is charged at more than nine times its real weight. The dense carton is charged on dead weight because it takes up so little space. The pallet is also charged on cubic weight, even though it weighs 300 kg.
The factor changes the result. At IATA’s 6,000 divisor, the same pallet’s volumetric weight is about 271 kg. That’s below its dead weight, so by air it would be charged at 300 kg.
How to reduce cubic weight
- Right-size your boxes. Use the smallest carton that fits the item plus its protective packing. Cutting the bulky carton above to 0.50 × 0.40 × 0.40 m drops its cubic weight from 37.5 kg to 20 kg.
- Cut wasted space. Empty space inside a box counts towards cubic weight just like product does. Trim tall boxes down or choose cartons with adjustable height.
- Use satchels for soft goods. Clothing and other soft goods that won’t be damaged by squashing often travel well in a satchel. See the guide on how to package parcels for courier and freight.
- Combine items. Several small items in one well-filled carton can cost less than separate boxes.
- Stack pallets squarely. Keep cartons inside the pallet footprint with no overhang, and build a flat, even top. The guide on how to prepare pallets for freight covers this step by step.
- Measure and weigh properly. Guesses go wrong in both directions. Real figures give you a real price.
What to send for an accurate freight quote
A quote is only as good as the details behind it. Send these with every request:
- Pick-up and delivery addresses, or at least the suburbs
- The number of items and the type of each: satchel, carton, pallet or loose item
- Length, width and height of each item, in centimetres or metres
- Dead weight of each item, in kilograms
- What the goods are, and whether they’re fragile or can be stacked
- Access at each end, such as a loading dock, forklift or stairs
- When it needs to be picked up and delivered
If you send the same products often, keep a list of their packed sizes and weights. It makes every quote faster.
How PBR Express Logistics can help
We quote every job first and confirm the price before pick-up. Our road freight service moves cartons, pallets and bulky items, as a one-off or on a regular run. For documents, satchels and small cartons that need to arrive the same business day, use our same-day courier service. Send your route, sizes and weights through our online freight quote form, or call 0485 752 618.
FAQs
Is cubic weight the same as volumetric weight?
Yes. Cubic weight, volumetric weight and dimensional weight all describe a weight calculated from an item’s size. In Australia you’ll often hear “cubic weight”, while air freight usually says “volumetric weight”. The conversion factor can still differ between carriers and services.
Does cubic weight apply to small parcels?
It depends on the carrier. Australia Post generally doesn’t apply cubic charges to parcels under 1 kg sent on non-contract terms, such as through MyPost Business. It reserves the right to, though, especially for large or odd-shaped items. Other carriers set their own rules, so check before you send.
How do I convert centimetres to metres for cubic weight?
Divide each measurement by 100. A 40 × 30 × 20 cm carton becomes 0.40 × 0.30 × 0.20 m, which is 0.024 m³. At 250 kg/m³, that’s a cubic weight of 6 kg.
Why did my freight cost more than the weight suggested?
It was most likely charged on cubic weight. A box that’s large for its weight has a cubic weight above its scale reading, and the carrier bills the higher figure. Measuring the packed item and right-sizing the box is the best fix.
