The waterfall: every line a three-parcel merge can produce
A merge does not produce 1 charge; it produces a short waterfall, and only the bottom of that waterfall is international freight. Reading the lines in order is what tells you whether combining 3 parcels into 1 box produced the saving you expected.
| Line | Charged per | Set by |
|---|---|---|
| Domestic delivery to the warehouse | parcel, from the seller | the seller, and paid before the merge stage |
| Warehouse handling and merge work | merge operation, or per line added | the agent, from its published terms |
| Repacking and packaging removal | box, when shoeboxes or filler come out | the agent, priced per operation |
| Chargeable weight | the greater of scale weight and volumetric weight | the carrier formula and the divisor it uses |
| Surcharges, such as fuel or peak season | shipment, on the carrier schedule | the carrier, revised on its own timetable |
| Customs duty, tax and handling | consignment, at the border | an authority, plus whoever advances the money |
The order matters because the first 3 lines are decided at the warehouse and the last 3 are decided after it. A decision taken while the box is still open costs less than the same decision taken at the counter, which is the whole reason the [merge and pack stage](/steps/merge-parcel/) is worth slowing down for.
No figure is published here for any of those 6 lines, because each one is set by a different party and revised on a different schedule. What can be published is the arithmetic, and the arithmetic is where the surprises live.
Before paying freight, ask for each line separately. A single total hides which of the 6 grew, and that answer decides whether the merge was worth it.
What each line carries, and which variables move it
The shares move with 3 variables, and none of them is the number of items. Chargeable weight, destination zone and packing volume do most of the work, which is why 3 light bulky items can cost more to move than 5 heavy compact ones.
Chargeable weight is the 1st thing to understand, because it is not the weight on the scale. Where a carrier takes the greater of scale weight and volumetric weight, a box that is mostly air is billed on its dimensions, and the divisor that turns centimetres into kilograms belongs to the carrier.
- Scale weight: what the box weighs on the warehouse scale, packaging included.
- Volumetric weight: length × width × height in cm, divided by the carrier divisor.
- Chargeable weight: the greater of the 2, and the figure the freight line is calculated on.
Cubic size is the second variable, and it is the one a buyer can still change at the warehouse. A box measuring 48 × 38 × 32 cm holds 58,368 cm3, which at a divisor of 5000 is 11.67 kg of volumetric weight against 6.2 kg on the scale.
Two buyers with identical orders can see different freight lines for the same box, because a divisor of 5000 and a divisor of 6000 read 11.67 kg and 9.73 kg from the same 58,368 cm3. Neither quote is an error; they are 2 formulas, and that is the first thing to check when 2 quotes sit far apart.
The 3rd variable is the destination zone, which no amount of packing changes. Zone belongs to the address, so 2 identical boxes sent to 2 addresses in the same country can land in different brackets, and the [chargeable weight tool](/rig/chargeable-weight/) exists to keep the first 2 variables visible while you compare quotes.
Which lines move, and which are already settled
Three of the 6 lines respond to decisions a buyer can still make, and 3 of them do not. Separating those 2 groups is the whole of cost compression in a merge.
- Compressible: warehouse handling, where the number of operations matters more than the number of items.
- Compressible: repacking, where removing shoeboxes and filler changes volume and therefore volumetric weight.
- Compressible: chargeable weight itself, since a smaller box for the same goods weighs less in volumetric terms.
- Fixed: domestic delivery, which was already paid to bring the items to the warehouse.
- Fixed: the destination zone, which belongs to the address rather than to the parcel.
- Fixed: duty and tax at the border, which belong to the goods and to the declared value rather than to the box.
The repack is the lever with the largest mechanical effect. Dropping the same jacket and 2 pairs of shoes into a smaller box changes nothing about the goods and a lot about the freight, which is why asking for box dimensions before payment is routine rather than fussy.
Ask which operations the fee covers before agreeing to them. A quote that bundles the merge, the repack and the removal of packaging into 1 figure cannot be compared with a quote that lists them separately, and 2 quotes that cannot be compared are 1 quote too many.
Handling answers a different question, namely how many operations the warehouse is asked to perform. A merge requested in 1 message with a clear instruction list costs less to process than the same merge requested across 4 separate messages.
After the repack: what the same goods weigh
Take the same 3 parcels and the same 6.2 kg of goods, then change only the box. The example below is our own arithmetic rather than a quotation, and it shows where a saving can come from.
| Measure | Before the repack | After the repack |
|---|---|---|
| Box dimensions | 48 × 38 × 32 cm | 48 × 32 × 24 cm |
| Volume | 58,368 cm3 | 36,864 cm3 |
| Volumetric weight at a divisor of 5000 | 11.67 kg | 7.37 kg |
| Scale weight of goods and box | 6.2 kg | 6.2 kg |
| Chargeable weight, the greater figure | 11.67 kg | 7.37 kg |
The gap is 4.30 kg of chargeable weight on identical goods. Multiply that by the per-kilogram rate for your zone and the freight line moves by that amount, while the item cost, the domestic legs and the customs treatment of the goods stay exactly where they were.
What does not change is the risk profile, and 2 things get worse at the same time. A smaller box with less filler protects less, and a repack that removes a shoebox also removes the easiest place to hide a defect from a photograph, which makes it a trade rather than a pure saving.
Ask for the final box dimensions and the chargeable weight in the same message as the freight quote, since together they decide the largest line.
Three cases where the separate boxes cost less
There are 3 situations where 3 separate boxes cost less than 1 combined box, and each of them is about a bracket rather than about weight.
- When the combined box crosses into a higher weight bracket that prices the whole shipment at the higher rate.
- When the volumetric weight of the combined box exceeds the sum of the 3 boxes, which happens when the combined box is mostly air.
- When adding the declared values onto 1 entry pushes the consignment over a relief threshold that the 3 parcels each stayed under.
The third case is the one buyers miss, because it does not look like a shipping decision at all. Merging places the declared values of 3 purchases on 1 entry, so a threshold that none of them crossed alone can be crossed by the consignment as a whole; thresholds differ by destination and are revised from time to time, which puts the current position with the official source rather than in a forum thread.
Arithmetic covers the 2nd case. Where 3 boxes of 40 × 30 × 20 cm each hold 24,000 cm3, the 3 together hold 72,000 cm3 before any packaging between them is removed, and a combined box that fails to come in below that figure is not saving volume at all.
Run the comparison as 2 quotes rather than as an argument. Ask for 1 combined quote and 3 separate quotes, then compare chargeable weight and the number of handling operations on each; the [merge optimiser](/rig/merge-optimiser/) is built to hold both versions side by side.
The three figures to collect before you decide
Three figures decide the comparison, and all 3 can be collected before the freight is paid rather than after it.
- The chargeable weight of the combined box, and the chargeable weight of each of the 3 boxes alone.
- The box dimensions after the repack, in cm, since volume rather than weight is what usually grows in a merge.
- The declared values of the 3 parcels added together, because that is the figure a border sees once the box is combined.
Then compare like with like. Freight on a combined box is 1 line, while freight on 3 boxes carries 3 handling operations and often 3 separate customs entries, and the second arrangement is simpler to argue about if 1 of the 3 items turns out to be wrong.
The last point is the practical one. A combined box is 1 shipment with 1 tracking number, so a problem with 1 item can hold up the other 2, while 3 boxes fail independently; independence has a price, and it is worth comparing that price with the saving before the [freight is paid](/steps/pay-freight/).
If chargeable weight barely moves and the combined declared value crosses a threshold, 3 boxes are the simpler arrangement.
Worked example: the same 6.2 kg of goods in a 48 × 38 × 32 cm box carries 11.67 kg of volumetric weight at a divisor of 5000, and the same goods in a 48 × 32 × 24 cm box carries 7.37 kg, so the box rather than the contents decides 4.30 kg of the freight line.
This note explains the mechanics; the list is where the items are.