How to calculate dimensional weight for multiple boxes
For parcel rules applied per piece, work out the billable weight of each carton, multiply it by the quantity and add the lines. Do not compare the shipment’s total scale weight with its total volumetric weight instead.
- Each carton
- The higher of scale and volumetric weight, rounded up to the carrier’s step
- Shipment
- The sum of billed weight per carton × quantity
- Common mistake
- Comparing totals: 50 kg instead of 56.5 kg in the example below
- Exceptions
- DHL Express rounds a shipment over 30 kg up to a whole kg; air cargo and some freight services use the total volume
The calculation, carton by carton
volumetric weight = length × width × height ÷ divisor billed per carton = the higher of scale and volumetric weight, rounded up to the step shipment billable weight = Σ (billed per carton × quantity)
Sides are measured on the outside of the carton. The divisor, any rounding of the sides and the weight step come from the carrier’s rule for your service. The example below uses 5000 cm³/kg and 0.5 kg steps.
Worked example: three carton types, six boxes
| Carton | Qty | Size (cm) | Scale (kg) | Volumetric (kg) | Billed each (kg) | Line total (kg) |
|---|---|---|---|---|---|---|
| Box A · mugs | 3 | 40 × 30 × 25 | 4 | 6 | 6 | 18 |
| Box B · cushions | 2 | 60 × 40 × 30 | 8 | 14.4 | 14.5 | 29 |
| Box C · books | 1 | 30 × 25 × 20 | 9.5 | 3 | 9.5 | 9.5 |
| Shipment | 6 | 37.5 total | 56.5 |
The mugs and cushions are light for their size, so they are billed on volume: 14.4 kg rounds up to 14.5 kg for each cushion box. The books are dense, so their 9.5 kg scale weight counts. The shipment bills 56.5 kg against 37.5 kg on the scale: 19 kg of it is air.
Open this example in the calculator
Why comparing totals gives the wrong answer
Add up the same shipment first and you get 37.5 kg on the scale and 49.8 kg of volumetric weight. Taking the higher total and rounding it gives 50 kg, which is 6.5 kg short of the real 56.5 kg.
The heavy book box hides the air in the light boxes: its scale weight is 6.5 kg above its volumetric weight, and in a lumped total that surplus cancels part of the volume the other boxes are charged for. A carrier that bills per piece never makes that trade, and it rounds each piece up on its own.
Cartons in centimetres, a rule in inches
US parcel rules bill in inches and pounds and round each side up to a whole inch. Convert each carton first, then round: the 40 × 30 × 25 cm mug box is 15.75 × 11.81 × 9.84 in, billed as 16 × 12 × 10 in = 1,920 in³, ÷ 139 = 14 lb under the UPS Daily Rates rule. The whole example shipment comes to 131 lb under that rule. Typing centimetres into an inch calculator, or rounding before converting, gives a different and wrong number.
When the whole shipment is measured instead
Air cargo and some multi-piece or freight services work out chargeable weight from the total volume of the consignment rather than per carton, and some contracts set their own rule. Use your rate guide to see which one applies. The calculator here works per carton, which is how UPS, FedEx, USPS and DHL Express bill individual parcels. DHL Express then rounds the shipment total once more: over 30 kg, up to the next whole kg (DHL rule); FedEx can rate multi-piece shipments on total weight (FedEx Multiweight).
Paste the cartons from a spreadsheet
The calculator reads rows copied from Excel, Google Sheets or a WMS export, with or without a header row. These columns work as they are:
name qty length width height weight Box A · mugs 3 40 30 25 4 Box B · cushions 2 60 40 30 8 Box C · books 1 30 25 20 9.5
Open the calculator, choose Paste from spreadsheet and check the preview before adding them. Lines with a missing size or weight are listed and left out, never counted silently.
Related
Last updated: 28 October 2026. Billable weight only: surcharges, minimum charges and your negotiated rates are not included.