Published: September 9, 2026 · Updated: September 9, 2026 · Reading time: ~8 minutes
International air freight charges are determined by chargeable weight — not by what your shipment weighs on a scale, and not by its physical volume alone. Chargeable weight is whichever is greater between actual weight and volumetric (dimensional) weight. When you ship light but bulky cargo, volumetric weight almost always wins — and that is where bubble-split (volume discount) calculations come in.
This guide, prepared by Goodhope Freight — a China-based international freight forwarder with NVOCC license GD20230925153335 — walks you through every formula you need, then shows a real shipment we priced: auto parts shipped from Jiangsu, China, to Conakry, Guinea (CKY) on Ethiopian Airlines (ET).
Chargeable weight is the figure the airline multiplies by the air freight rate to produce your invoice. It is the greater of two values:
The logic is simple: an aircraft charges you for space, not just mass. A pallet of foam pillows weighs 80 kg but occupies the space of 600 kg of steel. The airline bills you for the space you consume, hence volumetric weight exists.
Quick rule of thumb: if your cargo is heavy and compact (e.g. metal parts, machinery), you pay by actual weight. If your cargo is light and bulky (e.g. apparel, furniture, empty boxes), you pay by volumetric weight.
Under the IATA general cargo standard, 1 CBM = 167 kg of chargeable weight. The formula in centimetres is:
Volumetric Weight (kg) = L × W × H (cm) ÷ 6000
Because 1 CBM = 1,000,000 cm³, and 1,000,000 cm³ ÷ 6000 cm³/kg = 166.67 kg ≈ 167 kg.
Some low-density or special-cargo rates use a different factor (e.g. 1 CBM = 200 kg or 1 CBM = 250 kg). Always confirm the factor on your air waybill contract before shipping. For general air freight out of China, 167 kg/CBM is the default.
Need to compare with other shipping modes? See our full volumetric weight guide for DHL, FedEx, UPS, and TNT.
A bubble-split — also called a volume discount or colloquially a “half-bubble” — is what Chinese freight forwarders apply when your cargo is bulky but light. Instead of charging you the full volumetric weight, the forwarder splits the “bubble” (the gap between volumetric and actual weight) so the customer only pays for a portion of it.
There are four common scenarios. Below, A = actual weight, V = volumetric weight.
No bubble split means the airline charges the full volumetric weight when it exceeds the actual weight. You pay the maximum of the two.
Chargeable Weight = max(A, V)
Example: 50 kg actual, 187 kg volumetric → chargeable = 187 kg.
The most common split on China-origin air freight. The forwarder charges half of the “bubble” (the gap) on top of the actual weight.
Chargeable Weight = A + (V − A) ÷ 2
Equivalent form: (A + V) ÷ 2
Example: 50 kg actual, 187 kg volumetric → 50 + (187 − 50) ÷ 2 = 50 + 68.5 = 118.5, rounded up to 119 kg. (Airlines typically round chargeable weight up to the next whole kg.)
Offered on lighter-density cargo (foam, hollow plastic items, garments in large cartons). The forwarder charges only one-third of the bubble.
Chargeable Weight = A + (V − A) ÷ 3
Same example: 50 + (187 − 50) ÷ 3 = 50 + 45.67 ≈ 96 kg (rounded up).
Used when the airline agrees to a moderate discount. Two-thirds of the bubble is added on top of the actual weight.
Chargeable Weight = A + (V − A) × 2 ÷ 3
Same example: 50 + (187 − 50) × 2 ÷ 3 = 50 + 91.33 ≈ 142 kg (rounded up).
| Bubble Type | Formula | Chargeable Weight | Cost vs. Full Volumetric |
|---|---|---|---|
| No bubble split | max(50, 187) = 187 kg | 187 kg | 100% (baseline) |
| Two-thirds bubble | 50 + (187−50) × 2/3 ≈ 142 kg | 142 kg | ~76% (24% savings) |
| Half bubble | 50 + (187−50)/2 ≈ 119 kg | 119 kg | ~64% (36% savings) |
| One-third bubble | 50 + (187−50)/3 ≈ 96 kg | 96 kg | ~51% (49% savings) |
Important: Not all airlines or routes offer every bubble split. Half-bubble is the most widely available; 1/3 and 2/3 bubble are typically limited to specific carriers, agents, or seasonal promotions. Always confirm the split type before booking with your forwarder.
Below is a recent air freight shipment our team priced and tendered. Names and rates are reproduced exactly as quoted to the customer.
| Rate Break | Rate (RMB/kg) | Conditions |
|---|---|---|
| +45 kg and above | RMB 50 / kg | Standard rate |
| +100 kg and above | RMB 48 / kg | Half-bubble included; handling included; customs declaration & B/L excluded; cargo to be self-delivered to Shanghai (PVG) |
| Passenger-flight uplift (daily) | + RMB 1 / kg | Additional surcharge if routed via passenger flights instead of the weekly freighter |
| PVG local charges | RMB 350 (flat) | Terminal handling at Shanghai Pudong |
Service notes: The PVG–CKY route is served primarily by wide-body passenger aircraft (ET), with one weekly freighter rotation. Indicative door-to-door transit time after uplift: 5–7 days.
This shipment qualifies for the +100 kg half-bubble rate because the volumetric weight (187 kg) is much higher than the actual weight (50 kg). Here is exactly how we arrived at the cost:
Step 1 — Calculate the volumetric weight.
Volumetric Weight = 1.12 CBM × 167 kg/CBM = 187.04 kg → round up to 187 kg
Step 2 — Determine the chargeable weight without any bubble split.
Compare volumetric (187 kg) vs. actual (50 kg). Volumetric wins.
Chargeable (no split) = max(50, 187) = 187 kg
Step 3 — Apply the half-bubble split.
First, find the “bubble” (the excess volumetric weight over actual weight):
Bubble = V − A = 187 − 50 = 137 kg
Then charge for half of that bubble, on top of the actual weight:
Half-Bubble Chargeable = A + Bubble ÷ 2 = 50 + 137 ÷ 2 = 50 + 68.5 = 118.5 kg
→ rounded up to 119 kg
Step 4 — Multiply by the quoted rate.
At the +100 kg all-in rate of RMB 80 / kg (the published 48 RMB/kg plus security surcharge, fuel surcharge, customs declaration fee, and B/L fee — see note below):
Total Air Freight Cost = 119 kg × RMB 80 / kg = RMB 9,520
The headline rate of RMB 48/kg in the quote covers the freight only, with half-bubble and warehouse handling included. The all-in rate you actually pay (RMB 80/kg in this case) typically adds on:
Always ask your forwarder for the all-in rate per kg, not just the base freight rate. The all-in figure is what determines your real landed cost.
If this shipment had been priced without the half-bubble split, the chargeable weight would have been 187 kg, and the cost would have been RMB 80 × 187 = RMB 14,960. By applying the half-bubble split, the customer saved RMB 5,440 (≈ 36%) on a single shipment.
1 CBM = 167 kg under the IATA general cargo standard. The formula is: Volumetric Weight (kg) = L × W × H (cm) ÷ 6000.
Because for most light, bulky cargo out of China, the half-bubble split is the standard market practice on negotiated air freight contracts. If you are not getting a half-bubble quote, you are likely paying retail.
No. Volumetric weight is the carrier’s standard formula (167 kg/CBM). The bubble split is an additional discount applied by the forwarder — it sits on top of the volumetric-vs-actual comparison.
You will pay by actual weight. The bubble split is irrelevant because actual weight already exceeds volumetric weight. No split, no discount needed.
Generally no — the airline bills the greater of actual or volumetric weight. However, surcharges (fuel, security, peak-season) are added on top of that base, which can make the total invoice feel larger than expected.
No. Couriers use a different factor (typically 5000 rather than 6000), so their volumetric weight comes out higher. See our DHL/FedEx/UPS/TNT volumetric weight guide for details.
Send us your carton dimensions, gross weight, and destination airport. We will reply with an all-in rate — including bubble split, fuel surcharge, and PVG local charges — within 24 hours.
