Does merging two parcels actually save money?
Compare the chargeable weight and the postage of shipping separately against merging, including the merge fee.
Parameters last checked · defaults are templates, not quotes.
Merging removes repeated minimum charges and consolidates packing, but it also removes air gaps that were doing useful work: the merged carton can flip the charge onto volumetric weight.
Enter the parcels you are holding and the merge conditions you were quoted, then read both billable weights rather than only the saving.
A saving in dollars is the difference between two modelled invoices, and both are priced with the same first-kilogram and continuation bands. The continuation step is charged in whole kilograms, so a merged parcel of 3.1 kg is billed like 4 kg. That is the lever worth testing before committing, because the figure moves in steps rather than smoothly. Compare the merged billable weight with the next whole-kilogram boundary, and remember that the step responds to mass only while mass decides the bill, not while volume does.
Where the merged volume, reduced by the fill factor, still exceeds the combined mass, the charge flips to the volumetric side and the note beneath the result says so. The saving then rests on an assumption you supplied: 0.9 describes a tightly packed carton, lower values a realistic one. Two checks follow. Set the fill factor at the pessimistic end and see whether the saving survives, and confirm from the quote that the merge fee is charged once rather than per parcel, since per-parcel fees are what merging removes.
Parcel merge comparison
Parcels at the warehouse
How tightly the warehouse can pack: 0.7 conservative, 0.9 optimistic.
Separate or merged
Merging saves
$16.50
After merging, volumetric weight decides the charge — check the packing density before you commit.
| Option | Chargeable weight | Postage |
|---|---|---|
| Ship separately | 6,500 g | $91.00 |
| Merge into one | 5,850 g | $74.50 |
How to read the result
- A positive saving is not automatic — when volumetric weight takes over, merging can cost more than shipping separately.
- The fill factor models how tightly the warehouse can pack. 0.9 is optimistic; 0.7 is conservative.
- Merging also changes risk: one lost parcel instead of two, but the whole value travels together.
- Fees are per parcel on most services, so merging removes a per-parcel charge as well as postage.
- Both columns are priced with the same first-kilogram and continuation bands, so part of any saving is a repeated minimum charge removed rather than postage on weight.
Formula, source and caveat
merged volume = Σ(parcel volumes) × fill factor
- Source
- Physical packing model used by this tool.
- Caveat
- Real packing rarely reaches the modelled density.
cost = first-kilogram price + continuation price × extra kilograms
- Source
- Published line structure.
- Caveat
- Continuation steps vary between per-500 g and per-kg.
Questions this tool raises
- Should I always merge to save the per-parcel fee?
- Only when the combined parcel stays under the weight where volumetric weight takes over.
- Can anything not be merged?
- Restricted categories are often kept apart, and some services will not mix batteries with general cargo.
- Does merging delay dispatch?
- It adds a handling step. Expect roughly one extra day at the warehouse.