A 20GP holds 33.2 CBM, a 40GP holds 67.7 CBM, and a 40HQ holds 76.4 CBM — on paper. In practice, plan on 25–28 CBM of usable space in a 20GP and 60–65 CBM in a 40HQ. The gap is stacking: cartons never fill a steel box the way water does.
The three standard containers
These are typical ISO internal dimensions and max payloads. Carriers vary slightly, so treat the figures as planning numbers and confirm with your forwarder.
| Container | Volume / max payload |
|---|---|
| 20GP | 33.2 CBM / 28,200 kg |
| 40GP | 67.7 CBM / 26,800 kg |
| 40HQ | 76.4 CBM / 26,500 kg |
The 40HQ is the workhorse for light cargo. It costs only a little more than a 40GP and holds about 13% more volume, because it is 30 cm taller inside. The 20GP is the choice when the cargo is heavy: its payload limit is the highest of the three.
Worked example: volume math
Cartons of 60 × 50 × 40 cm, 12 kg each. One carton is 0.12 CBM.
- 20GP: 33.2 ÷ 0.12 = 276 cartons by volume.
- 40GP: 67.7 ÷ 0.12 = 564 cartons by volume.
- 40HQ: 76.4 ÷ 0.12 = 636 cartons by volume.
Weight is not the limit here. 276 cartons × 12 kg = 3,312 kg, far under the 20GP payload limit of 28,200 kg. Light cargo is always limited by volume, not weight.
Worked example: stacking math
Volume math assumes cartons melt into every corner. Real cartons stack in layers. Take the same 60 × 50 × 40 cm carton in a 20GP (inside 5.90 × 2.35 × 2.39 m):
- Along the length: 5.90 ÷ 0.60 = 9 cartons.
- Across the width: 2.35 ÷ 0.40 = 5 cartons.
- Layers high: 2.39 ÷ 0.50 = 4 layers.
- Total: 9 × 5 × 4 = 180 cartons, or 21.6 CBM.
Volume math says 276 cartons; stacking says 180. The honest plan is 180–200 cartons, roughly 22–24 CBM of usable space. The other 30% is air between cartons, uneven layers, and space you cannot reach.
When weight decides instead
Heavy cargo hits the payload limit long before the box is full. Take the same carton at 100 kg each:
- 20GP by volume: 276 cartons. By weight: 28,200 ÷ 100 = 282 cartons. Volume still binds — barely.
- At 150 kg per carton: 28,200 ÷ 150 = 188 cartons by weight, against 276 by volume. Weight binds. The container leaves with 188 cartons and 10 CBM of empty air.
The rule: whichever limit you hit first is your real capacity. Check both numbers every time — the calculator above does.
Which container to book
- Under 25 CBM: a 20GP is usually the cheapest full container. Under 15 CBM, compare against LCL.
- 25–60 CBM: a 40GP or 40HQ. The 40HQ costs little more and holds more.
- Over 60 CBM: a 40HQ, or two containers. Above 76 CBM you need a second box.
- Heavy cargo over 26 tonnes: a 20GP, because its payload limit is the highest. A 40HQ cannot legally carry what a 20GP can.