Per-Piece vs Per-Shipment Chargeable Weight
The same boxes bill differently by courier vs air cargo. Switch the divisor chips to see it.
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.
Worked example — same two boxes
Two cartons: Box A = 40 × 32 × 50 cm, 8 kg. Box B = 20 × 20 × 20 cm, 5 kg.
Isolating the rule (same ÷5,000 divisor)
- 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.
In the real world (÷5,000 courier vs ÷6,000 air cargo)
Couriers use ÷5,000 and bill per piece → 17.8 kg. Air cargo uses ÷6,000 and bills per shipment: total volumetric = 108,000 ÷ 6,000 = 18.0 kg vs 13.0 kg actual → 18.0 kg. Here the smaller divisor advantage of air cargo is outweighed by this box mix — which is exactly why you should run both. Use the air freight calculator and the express calculator to reproduce each number, and see every carrier’s divisor on the DIM divisor chart.
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.