Does 1 kg off case weight always cut the air bill?

A: No. Below volumetric weight the chargeable figure does not move and the saving is zero; above it, each kilogram is worth 38 CNY.

What is the difference between dividing by 6000 and 5000?

A: The same case reads 13.8 kg at 5000 and 11.5 kg at 6000, a gap of 2.3 kg — express costs about 20% more on the same box.

Is a 3.5 to 3.0 mm wall worth it?

A: Only on heavy air cargo. It saves 0.45 kg and 17 CNY while pushing corner cracking at -20 °C from 2% to 11%.

An FCL will not fill. Is it weight or volume?

A: Volume, usually. 855 cases use 12% of the 26 t limit; weight only starts to bite past 25 kg of kit per case.

Case Weight and Freight: What 1 kg Saves

Quick answer: Case weight only moves the freight bill when gross weight passes volumetric weight. A 626 × 442 × 250 mm case cubes out at 11.5 kg, so a 3.6 kg shell holding 6 kg of kit still ships at 11.5 kg and 1 kg saved is worth nothing; at 13.5 kg gross, 1 kg off saves 38 CNY by air.

Four Sources of Case Weight
Chargeable Weight vs Volumetric
What 1 kg Saves in Three Scenarios
Four Ways to Drop Weight, and Their Cost
Checking Weight on a Quote
FAQ

1. Four Sources of Case Weight

Split 3.60 kg and it reads: lid 1.05, base 1.42, hardware 0.68, foam 0.45. Plastic comes to 2.47 kg, or 69%; the other 31% is latches, hinges, handle mounts and liner, which is the part quotes forget. Case weight has to be booked in those four lines, or a weight-reduction programme ends up thinning foam.

Run the same outline at a 5.0 mm wall and plastic rises to 3.53 kg, the whole case to 5.10 kg. Of the extra 1.50 kg, 1.06 is wall and 0.44 is ribs thickened to match. Ribs grow with the wall, which is why two quotes rarely agree.

Rotomoulded PE at the same size lands at 7.80 kg, 2.2 times the injection-moulded PP. A uniform 6 mm wall buys a drop rating past 1.5 m, and costs case weight that needs two people to lift.

Part	Weight	Share	Detail
Lid	1.05 kg	29%	3.5 mm wall, two transverse ribs inside
Base	1.42 kg	39%	3.5 mm wall, eight floor ribs
Hardware	0.68 kg	19%	Two hinges, two latches, two handle mounts
Foam	0.45 kg	13%	30 mm, three bonded layers
Total	3.60 kg	100%	600 × 400 × 230, injection PP

2. Chargeable Weight vs Volumetric

Carriers bill the greater of actual and volumetric weight. Volumetric is the outline multiplied out and divided by a factor: 6000 for air freight, 5000 for express. At 62.6 × 44.2 × 25.0 cm the case measures 69,173 cm³, which is 11.5 kg by air and 13.8 kg by express.

The 3.6 kg shell is 31% of that 11.5 kg. Three tenths of an air bill pays for the case, seven tenths for the space it encloses. Shrinking the outline beats shaving grams every time.

Mode	Chargeable rule	This case	Rate	Per case
Air freight	L × W × H ÷ 6000	11.5 kg	38 CNY/kg	437 CNY
Express	L × W × H ÷ 5000	13.8 kg	52 CNY/kg	718 CNY
Sea LCL	W/M, 1 m³ = 1000 kg	0.0692 revenue ton	450 CNY/ton	31 CNY
40HQ FCL	Per container, 26 t limit	855 cases	15,800 CNY	18.5 CNY

Sea LCL takes the larger of the two: 0.0692 m³ becomes 0.0692 revenue tons against 0.0036 tons of actual weight, a factor of 19, so volume always wins. FCL follows the same logic — 855 cases at 3.6 kg is 3.1 t, 12% of a 26 t limit. On those two lanes case weight barely enters the calculation.

3. What 1 kg Saves in Three Scenarios

Scenario A, light cargo. Six kilos of kit plus a 0.9 kg carton gives 10.5 kg gross, still billed at 11.5 kg. Take case weight from 3.6 to 2.4 and the chargeable figure does not move: saving, zero.

Case weight and freight: vermilion case on its side, handle left, two hinge barrels offset half a pitch, plain lid, crisp parting line

Scenario B, heavy cargo. Nine kilos of kit gives 13.5 kg gross, billed at 13.5 kg, and 437 CNY becomes 513 CNY. Here every kilogram removed is worth 38 CNY by air and 52 CNY by express.

Scenario C, an overweight FCL. At 28 kg of kit the gross is 32.5 kg, 855 cases reach 27.8 t and the 26 t limit cuts the load to 800 cases. One kilogram off case weight allows 825 cases, 25 more per load, worth 0.08 USD a case.

Scenario	Gross	Chargeable	Saving per kg
A light	10.5 kg	11.5 kg	0
B heavy, air	13.5 kg	13.5 kg	38 CNY
C overweight FCL	32.5 kg	26 t limit	25 more cases

The dividing line sits at 7.0 kg of payload: 3.6 kg case plus 0.9 kg carton plus 7.0 kg of kit equals 11.5 kg, exactly the volumetric figure. Below that payload, case weight never reaches the billing formula.

4. Four Ways to Drop Weight, and Their Cost

Foam from 30 to 20 mm saves 0.42 kg and 10 mm of travel; at a 1.2 m drop the peak acceleration on 9 kg of kit climbs from 42 g to 58 g. Stainless hinges swapped for POM save 0.15 kg and show red rust at the pin after 96 hours of salt spray. Cutting floor ribs from eight to five saves 0.18 kg and lets the top case settle 1.2 mm under five-high stacking.

Case weight and freight: cream case closed and flat on white, full-width handle in end caps, arched finger scoop above, plain lid, rounded corners

Wall thickness from 3.5 to 3.0 mm saves 0.45 kg and costs the most: corner cracking at -20 °C rises from 2% to 11%. Do all four and case weight falls from 3.60 to 2.40 kg, a total of 1.20 kg.

What is 1.20 kg worth? Zero in scenario A, 45.6 CNY a case in scenario B, 30 extra cases per FCL in scenario C. The same reduction differs by an order of magnitude depending on the load, so count the payload before touching the wall.

5. Checking Weight on a Quote

Three checks: weigh by part, reconcile against density, ask about regrind. A 0.01 kg scale, three cases, median; lid and base weighed apart, because a single total usually hides 0.2 kg of missing hardware.

Density reconciles faster. PP at 0.91 g/cm³ puts 2.47 kg of plastic at 2714 cm³, which over a 3.5 mm wall is 0.78 m² of developed area. A drawing claiming 0.95 m² means the wall is overstated while the weight was quoted at 3.5 mm.

Ask about regrind separately. At 30% regrind the density holds and case weight stays identical, but stiffness at the same wall falls 8%, and the drop margin has to come out of thickness. The number on the scale is the same; the impact reserve is not.

Conclusion

Case weight is a two-step calculation: check whether gross passes volumetric, then see which billing line the saving lands on. A 626 × 442 × 250 mm case cubes at 11.5 kg, so under 7.0 kg of payload, going from 3.6 to 2.4 kg saves nothing at all; above that line each kilogram is worth 38 CNY. The outline decides the freight, and case weight only matters once gross crosses it.

This article discusses only the specification and design intent on the container (case) side, and does not cover any handling, loading or use of the contents.