How to Calculate CBM and Units Per Container (20ft/40ft/40HQ)
CBM (cubic meters) is calculated as length × width × height in meters for one unit, then multiplied by quantity: CBM = (L × W × H) × Qty. To estimate how many units fit in a container, divide the container's usable volume — about 28 m³ for a 20ft, 55 m³ for a 40ft standard, and 65 m³ for a 40HQ (roughly 85% of the theoretical maximum) — by the CBM of one unit. Always cross-check against the weight limit (about 28 tonnes payload), because dense loads hit the weight ceiling before the container is full.
Updated July 2026
The CBM formula (L × W × H)
CBM stands for cubic meter — the standard volume unit for ocean and LCL freight. The formula is simple:
CBM per unit = Length (m) × Width (m) × Height (m)
Total CBM = CBM per unit × Quantity
Three rules keep the number honest:
- Convert to meters first. Divide millimeters by 1,000 or centimeters by 100. A box of 600 × 400 × 300 mm is 0.6 × 0.4 × 0.3 = 0.072 m³. - Use external (outer) dimensions, not internal — freight is charged on the space the item occupies, including its walls. - Use the packed footprint. Foldable and nesting items ship at a fraction of their in-use volume; a folding crate that is 0.072 m³ open may fold to under 0.02 m³. Where a product page shows a CBM figure, that is the packed-for-shipping value — use it directly instead of recalculating.
On this network, specifications, dimensions and CBM are public for every SKU. Wholesale pricing and a landed CIF estimate unlock when you log in as an approved trade buyer.
Container capacity: 20ft vs 40ft vs 40HQ
Two numbers matter for each container: the theoretical volume (what the empty box measures) and the usable volume (what you can realistically load once you allow for access aisles, dunnage, load-securing and irregular shapes). Industry practice is 85–90% stow efficiency; we use ~85% for planning so estimates are conservative.
| Container | Internal L×W×H (approx) | Theoretical volume | Usable @ ~85% | Max payload (approx) |
|---|---|---|---|---|
| 20ft standard | 5.90 × 2.35 × 2.39 m | ~33.2 m³ | ~28 m³ | ~28,000 kg |
| 40ft standard | 12.03 × 2.35 × 2.39 m | ~67.7 m³ | ~55 m³ | ~28,600 kg |
| 40ft High Cube (40HQ) | 12.03 × 2.35 × 2.69 m | ~76.3 m³ | ~65 m³ | ~28,600 kg |
The 40HQ is the workhorse for plastic material-handling goods: same floor as a 40ft standard but ~30 cm taller, so tall, light, bulky items (bins, pallet boxes, folding boxes) gain a full extra tier of stacking. All figures are indicative planning values — the exact usable volume depends on how a specific item stacks or nests, and the per-product MOQ is confirmed when you apply for trade access. Minimum order is typically one full container load (1 FCL).
Estimating units per container
Two methods, from quick to precise:
1. Volume method (fast). Units per container = usable volume ÷ CBM per unit.
- A pallet at 0.18 m³ → 65 ÷ 0.18 = ~361 per 40HQ (by volume). - A logistics box at 0.042 m³ → 65 ÷ 0.042 = ~1,540 per 40HQ (by volume).
2. Stack/nest method (accurate). Volume math assumes cargo fills space like a liquid. Real rigid items leave gaps. For a truer count, work out how the item stacks and nests:
- Rigid stackable boxes/pallets: figure units per floor position (footprint ÷ container floor) × tiers that fit under the ceiling height. - Nesting containers: a nested stack collapses to a fraction of separated volume — count the nested stack height, not the single-unit height. - Folding boxes: count them folded flat; hundreds more fit than the open-volume math suggests.
Where a supplier-stated units-per-container figure exists, use it — it already reflects real stacking. Otherwise our estimates come from each product's CBM at ~85% stow efficiency. A 40' High-Cube container offers about 76.3 m³ of usable volume before the stow-efficiency discount.
The weight-vs-volume limit (which fills first?)
A container has two ceilings: volume (m³) and weight (payload, ~28 tonnes). You hit one before the other, and that one decides the real load.
- Light, bulky cargo (empty plastic bins, folding boxes, nesting crates) is almost always volume-limited — the container 'cubes out' long before it maxes weight. - Dense cargo (loaded pallets, thick-wall tanks, palletized stacks of heavy plastic) can be weight-limited — you hit ~28 tonnes with the container only part-full.
How to check: multiply your volume-method unit count × unit weight. If that exceeds ~28,000 kg, weight is your constraint — reduce the count until you are under the payload cap.
Chargeable weight (LCL/air): freight lines bill on whichever is greater — actual gross weight or volumetric weight. The sea/LCL convention is 1,000 kg per m³; air freight commonly uses 167 kg per m³. Light bulky plastics are therefore usually charged by the space they occupy, which is exactly why full-container (FCL) buying is the efficient route for this category.
Worked example (start to finish)
Goal: ship 1200×1000×150 mm plastic pallets in a 40HQ.
1. Convert: 1200 mm → 1.20 m, 1000 mm → 1.00 m, 150 mm → 0.15 m. 2. CBM per unit: 1.20 × 1.00 × 0.15 = 0.18 m³. 3. Volume count: 65 m³ usable ÷ 0.18 = ~361 pallets by volume. 4. Weight check: if each pallet is ~15 kg → 361 × 15 = 5,415 kg, well under 28,000 kg. Volume-limited — 361 stands. 5. Stack reality-check: pallets stack flat and interlock, so the volume count is close; round down to a clean planning figure and confirm on quote.
Swap in your own SKU's public CBM and unit weight and repeat. All numbers here are indicative planning values and are confirmed on quote.
Frequently asked
How do I calculate CBM?
Multiply length × width × height in meters for one unit, then multiply by quantity: CBM = (L × W × H) × Qty. Convert millimeters to meters by dividing by 1,000. Example: a 600 × 400 × 300 mm box is 0.6 × 0.4 × 0.3 = 0.072 m³.
How many CBM fit in a 20ft, 40ft and 40HQ container?
Theoretical volumes are about 33.2 m³ (20ft), 67.7 m³ (40ft standard) and 76.3 m³ (40HQ). In practice you load roughly 85% of that — about 28 m³, 55 m³ and 65 m³ respectively — to allow for access, dunnage and load-securing.
How many units fit in a container?
Divide the container's usable volume by the CBM of one unit. For example, 65 m³ ÷ 0.18 m³ ≈ 361 pallets in a 40HQ by volume. For rigid or nesting items, use a stack/nest count for accuracy, and always check the weight limit as well.
What is stow efficiency and why isn't the container 100% full?
Stow efficiency is the share of a container's volume you can actually use after aisles, dunnage, load-securing and irregular shapes. Industry practice is 85–90%; we plan at ~85% so estimates are conservative rather than optimistic.
What is the difference between the volume limit and the weight limit?
A container caps out on volume (m³) or weight (payload ~28 tonnes), whichever comes first. Light, bulky plastic goods usually cube out before hitting weight, while dense palletized loads can hit the ~28-tonne ceiling while still part-full. Check both.
Do I have to order a full container?
Minimum order is typically one full container load (1 FCL); the exact per-product MOQ is confirmed when you apply for trade access. Specifications, dimensions and CBM are public — wholesale pricing and a landed CIF estimate unlock when you log in as an approved trade buyer.