Per-Piece vs Per-Shipment Chargeable Weight
The same boxes bill differently by courier vs air cargo. Switch the divisor chips to see it.
Enter a box below and the billable weight appears here — the number your carrier charges you for, after its divisor, its dimension rounding and its weight rounding.
Enter a box below and the billable weight appears here — the number your carrier charges you for, after its divisor, its dimension rounding and its weight rounding.
Per-Piece vs Per-Shipment: The Short Answer
Express couriers bill per piece; IATA air cargo bills per shipment. That one difference can change your bill by 10–20% on a mixed consignment, with nobody making an error.
- Per-piece (DHL, UPS, FedEx, TNT International): chargeable weight = Σ max(volumetric, actual) for each box.
- Per-shipment (IATA air cargo): chargeable weight = max(Σ volumetric, Σ actual) across the whole shipment.
Per-Piece vs Per-Shipment Worked Example
Two cartons: Box A = 40 × 32 × 50 cm, 8 kg. Box B = 20 × 20 × 20 cm, 5 kg.
Per-Piece vs Per-Shipment with the Divisor Held Constant
- Box A volumetric: 64,000 ÷ 5,000 = 12.8 kg (beats 8 kg actual)
- Box B volumetric: 8,000 ÷ 5,000 = 1.6 kg (loses to 5 kg actual)
- Per-piece: max(12.8, 8) + max(1.6, 5) = 12.8 + 5 = 17.8 kg
- Per-shipment: max(12.8 + 1.6, 8 + 5) = max(14.4, 13.0) = 14.4 kg
Same boxes, same divisor — 3.4 kg difference purely from the billing rule. The light box’s spare volume gets “absorbed” by the heavy box only under the per-shipment rule.
Per-Piece Courier ÷5,000 vs Per-Shipment Air Cargo ÷6,000
Couriers use ÷5,000 and bill per piece → 17.8 kg. Air cargo uses ÷6,000 and bills per shipment: total volume 64,000 + 8,000 = 72,000 cm³ → 72,000 ÷ 6,000 = 12.0 kg volumetric vs 13.0 kg actual → 13.0 kg. Air cargo is 27% lighter on chargeable weight here, for the same two cartons.
This is not a coincidence of these numbers. Because max(Σ volumetric, Σ actual) is never greater than Σ max(volumetric, actual), and because the 6,000 divisor produces a smaller volumetric weight than 5,000, air cargo chargeable weight can never exceed courier chargeable weight on the same cartons. The two rules converge when every box is volume-heavy, and diverge most when dense and bulky boxes travel together.
Chargeable weight is not the whole price, though — air cargo rates, terminal handling and customs clearance are quoted separately, while courier rates usually bundle them. Reproduce each number with the air freight calculator and the express calculator, see every carrier’s divisor on the DIM divisor chart, then compare the all-in quotes.
When Per-Shipment Billing Costs You Money
The two rules only diverge when a shipment mixes densities. Knowing which case you are in tells you whether to shop the quote around at all.
| Consignment type | Per-piece vs per-shipment | What to do |
|---|---|---|
| All boxes volume-heavy (light & bulky) | Identical — volumetric wins everywhere | Compare divisors, not rules |
| All boxes dense (actual weight wins) | Identical — actual wins everywhere | Rule is irrelevant; shop on rate |
| Mixed dense and bulky | Per-shipment is cheaper, often 10–20% | Get an air cargo quote too |
Why Couriers Chose Per-Piece Billing
Express networks handle each parcel as an independent unit: separate scan, separate slot on the van, separate sortation path. Pricing each piece on its own worst case reflects that. Air cargo, by contrast, is built around consolidated ULDs (unit load devices) — the airline sells space and payload on a pallet or container basis, so comparing the consignment total matches how the capacity is actually consumed. Neither rule is arbitrary; each mirrors the cost structure underneath.
How to verify your own invoice
- List each carton with its dimensions and scale weight.
- Compute volumetric weight per carton using your carrier's divisor.
- Apply the per-piece rule: take max(volumetric, actual) for each carton, then sum. That should match a courier invoice.
- Apply the per-shipment rule: sum all volumetric, sum all actual, take the greater. That should match an air waybill.
- If the invoice matches neither, the discrepancy is usually dimension rounding, a reweigh adjustment, or a different contracted divisor — check the divisor chart and your rate card.
Both rules are implemented exactly in the calculator above — switch the divisor chips between ÷5,000 Express and ÷6,000 Air Cargo to see the same boxes billed each way. A step-by-step audit of a surprise invoice is covered in why your shipping bill is higher than expected.
Per-Piece vs Per-Shipment FAQ
Do couriers and air freight bill multi-piece shipments the same way?+
No. Express couriers (DHL, UPS, FedEx, TNT International) calculate the chargeable weight per piece: for each box they take the greater of volumetric and actual weight, then sum those. IATA air cargo bills per shipment: it sums all volumetric weights, sums all actual weights, and charges the greater of the two totals.
What is per-piece chargeable weight?+
Per-piece billing means chargeable weight = Σ max(volumetric, actual) for each box. A dense box and a light box are each judged on their own, so a heavy box cannot "absorb" the volume of a light one. This is how express couriers bill.
What is per-shipment chargeable weight?+
Per-shipment billing means chargeable weight = max(Σ volumetric, Σ actual) across the whole consignment. Dense boxes can offset the volume of light boxes because only the totals are compared. This is how IATA air cargo bills.
Which billing mode is cheaper?+
It depends on the mix. For consignments combining dense and bulky boxes, per-shipment (air cargo) is often cheaper because heavy boxes offset light ones in the totals. For uniformly bulky shipments the modes converge. Always compare both before booking.
Why do most calculators get this wrong?+
Many online calculators apply one rule to every mode, or sum volumetric weights without the per-piece max. That understates courier bills and can misstate air cargo. Our calculators implement both rules exactly.