A container looks full. The tally sheet says otherwise. Getting the loading calculation right before the truck leaves the yard avoids two expensive surprises: a container that comes back for one more log because it wasn’t actually full, or one that gets stopped at the port for exceeding its weight limit.
Standard container internal capacity
| Container | Internal volume | In cubic feet |
|---|---|---|
| 20ft Standard | 33.2 CBM | 1,172 CFT |
| 40ft Standard | 67.7 CBM | 2,392 CFT |
| 40ft High Cube | 76.3 CBM | 2,695 CFT |
These are the empty box’s internal dimensions. Timber never fills 100% of it — the real number depends on shape.
Fill factor: the number everyone forgets
Round logs stacked in a container leave triangular gaps between each round shape, however carefully they’re loaded. Sawn timber packs, stacked square on square, waste far less space.
| Cargo type | Typical fill factor | 20ft example | 40ft example |
|---|---|---|---|
| Round logs, loose stacked | 55-65% | 18-22 CBM | 37-44 CBM |
| Round logs, dunnage-packed | 60-70% | 20-23 CBM | 41-47 CBM |
| Sawn timber, strapped packs | 75-85% | 25-28 CBM | 51-58 CBM |
These ranges vary by log diameter, taper, and how much care goes into loading — treat them as planning figures, not a guarantee, and always confirm against your own loaded history for the species and mill you use.
Weight: the limit that often bites first
Every container has a maximum payload, set by the shipping line and the road/rail weight limits on the route — commonly in the range of 26-28 tonnes for a 20ft and 28-30 tonnes for a 40ft, though this varies by carrier and destination country and must be confirmed with your forwarder for the actual booking.
Timber density varies enormously by species:
- Teak (dry): roughly 650-750 kg/m³
- Pine/softwood: roughly 450-550 kg/m³
- Dense hardwoods (e.g. some African/SE Asian species): can exceed 900 kg/m³
For a dense hardwood, do the weight math before the volume math — a 20ft container of teak often hits its weight limit well before it looks visually full, while a container of light softwood usually runs out of space first with weight allowance to spare.
Worked example
20ft container, round teak logs, average density 700 kg/m³:
- Internal volume: 33.2 CBM
- Fill factor (loose-stacked round logs): 60% → 19.9 CBM of actual timber
- Weight at that volume: 19.9 × 700 = 13,930 kg
Well under a typical 20ft payload limit — this container is volume-limited, not weight-limited. The same container loaded with a 900 kg/m³ hardwood at the same 60% fill would weigh close to 17,900 kg, which starts to matter depending on the carrier’s actual limit for that route.
How to calculate it for your own load
- Get the true (Huber) CBM per piece from the tally — not the Hoppus figure, if your tally records both. Physical space needed is always true volume.
- Sum the true CBM of everything meant for the container.
- Divide by the container’s internal volume to get the fill percentage this load would need.
- Compare against a realistic fill factor for the shape (round vs sawn) — if the calculated fill percentage is higher than what round logs can realistically achieve, the load won’t physically fit as planned, regardless of what the CBM total suggests.
- Multiply total CBM by density to get estimated weight, and check it against the carrier’s actual limit for that container and route.
- Leave a margin. Planning to exactly the container’s theoretical capacity leaves no room for a size that measured slightly larger than tallied, or a log that doesn’t stack as expected.
Where this goes wrong in practice
- Using Hoppus CBM for the loading calculation — Hoppus volume is roughly 21% lower than true volume for the same log (see Hoppus vs true volume), so a loading plan built on Hoppus figures understates real space needed and the container comes up short.
- Assuming sawn-timber fill factors for round logs, badly overestimating how much actually fits.
- Planning to the container’s theoretical maximum, leaving no margin for real-world stacking.
- Skipping the weight check for dense species and discovering the overweight problem only at the port.
Keeping the tally and the load plan on the same numbers
The loading calculation is only as good as the tally feeding it — true CBM per piece, correctly summed, for exactly what’s going into that specific container.
In LumberLinq, every transport unit’s tally gives the true CBM total your staff actually measured, per container, so the loading estimate is built on the same figures as the invoice and the packing list — not a separate spreadsheet re-typed from memory.
Start free or see it in 15 minutes.
Frequently asked questions
How many CBM fit in a 20ft container? About 33.2 CBM internal volume, but round logs typically only occupy 55-65% of that in practice (18-22 CBM), due to the gaps between round shapes.
What limits a timber container first, weight or volume? Dense hardwoods usually hit the weight limit before the container looks full. Lighter softwoods usually run out of volume first.
Does Hoppus vs true volume change how many logs fit? No — physical space is always true (Huber) volume. Convert to Hoppus for the invoice only, if the contract requires it.
What is a fill factor? The real percentage of a container’s volume actually occupied once gaps between pieces are accounted for — always below 100%, more so for round logs than sawn packs.
Container capacities and weight limits vary by carrier, container condition and route — confirm the exact figures with your shipping line and forwarder before finalising a load plan.
Related: Hoppus vs true volume · Documents needed for a timber export shipment