KubovaHow to Calculate CBM (and Why It Isn’t Your Container Capacity)
By Kubova Team
CBM is the first number every freight quote asks for — and the one most people get subtly wrong, either by mixing up units or by assuming their CBM total is the same thing as container capacity. Here is the formula, the unit traps, and why a CBM number alone never tells you whether your cargo actually fits.
The CBM formula (and the unit trap)
CBM means “cubic metre”, so the whole formula lives in metres. Multiply the three sides of one carton in metres, then multiply by how many you have:
CBM = (Lm × Wm × Hm) × quantity
Almost every CBM mistake is a unit mistake. Carton sizes are usually quoted in centimetres, so convert first (divide each side by 100) or use the centimetre shortcut: multiply the three sides in centimetres and divide by 1,000,000.
Per carton: 0.6 × 0.45 × 0.4 = 0.108 CBM.
Shipment: 0.108 × 320 = 34.56 CBM.
Centimetre shortcut: (60 × 45 × 40) ÷ 1,000,000 = 0.108 — same answer.
CBM for mixed cartons
Most real shipments have several carton sizes. CBM is additive: calculate each line separately and sum them. Do not average dimensions — that quietly distorts the total.
| Line | Carton (cm) | Qty | CBM/carton | Line CBM |
|---|---|---|---|---|
| A | 50 × 40 × 30 | 200 | 0.060 | 12.00 |
| B | 60 × 45 × 40 | 120 | 0.108 | 12.96 |
| C | 40 × 30 × 25 | 300 | 0.030 | 9.00 |
| Total | — | 620 | — | 33.96 |
CBM vs container capacity — the part that bites
Here is the trap: 33.96 CBM looks like it fits a 20ft (≈33.2 CBM internal) or sits comfortably in a 40ft (≈67.7 CBM). Neither is safe to assume. The nominal figure is the container’s empty internal volume — what you would get if cargo poured in like water and filled every corner. Real boxes don’t.
We measured it: a light, well-proportioned 50×40×30 cm carton packed into each container with our engine. Even this tidy carton, with weight to spare, leaves 8–11% of the space empty:
| Container | Internal CBM | Cartons fit | Loaded CBM | Volume used |
|---|---|---|---|---|
| 20ft DC | 33.2 | 492 | 29.5 | 88.9% |
| 40ft DC | 67.7 | 1,040 | 62.4 | 92.1% |
| 40ft HC | 76.3 | 1,150 | 69.0 | 90.4% |
So a 34 CBM shipment will not fit a 20ft — its real ceiling is ~29.5 CBM for a carton this tidy, and less for awkward sizes — while it leaves room in a 40ft. CBM gets you in the right ballpark; it does not confirm a load.
From CBM to a real decision
CBM feeds three concrete decisions:
- FCL vs LCL. Below a breakeven volume, sharing a container (LCL) is cheaper; above it, a dedicated container (FCL) wins. CBM is the input — see the FCL/LCL breakeven.
- How many containers. Divide realistic loaded CBM into your total — but verify the actual layout, because a load that “just spills” often consolidates back into one. See avoiding a second container.
- Freight cost. CBM (or weight, whichever is greater) sets the chargeable amount.
The honest part
CBM is necessary but not sufficient. It is a volume total, not a loading plan — it can’t see orientation, stacking rules, the door opening or weight limits. When the number decides a booking, don’t divide CBM by a nominal figure and hope; lay the actual cargo out and let the geometry answer. Our calculator does exactly that, and it never overflows a container’s real dimensions to flatter the result.
Turn your CBM into a real load plan
Enter your cartons and container — get the exact fit in 3D, free, no card.
Related reading
- CBM, FCL and LCL: the exact volume where FCL wins.
- Volume vs weight: which container limit hits first.
- What a good container fill rate actually looks like.
Sources & method
- Container internal volumes: Kubova standard catalogue, per the pier2pier user guide §7.3 (20 DC ≈ 33.2, 40 DC ≈ 67.7, 40 HC ≈ 76.3 CBM).
- Loaded-CBM figures: measured by packing a 50×40×30 cm carton through the Kubova packing engine on 2026-06-17. Your fill varies with carton size and mix — compute your own in the calculator.
- Volumetric-weight convention (1 CBM = 1,000 kg for sea LCL) is the common carrier rule; confirm the exact divisor with your forwarder.
Frequently asked questions
How do you calculate CBM?
CBM (cubic metres) = length × width × height, with every dimension in metres. For one carton of 50 × 40 × 30 cm, convert to 0.5 × 0.4 × 0.3 = 0.06 CBM. Multiply by the quantity: 200 of those cartons = 12 CBM. If your dimensions are in centimetres, the shortcut is (L × W × H in cm) ÷ 1,000,000.
What is CBM in shipping?
CBM is the total volume of your cargo in cubic metres. Freight is priced on whichever is greater — actual weight or volumetric weight — and CBM is how the volume side is measured. It also drives the FCL-vs-LCL decision and tells you roughly how much container space a shipment needs.
How many CBM fit in a container?
By internal volume: a 20ft holds about 33.2 CBM, a 40ft about 67.7 CBM, and a 40ft High Cube about 76.3 CBM. But you can never load to that figure — real loads reach roughly 85–92% of it depending on cargo. We measured a tidy 50×40×30 cm carton with the engine: 29.5 CBM loaded into a 20ft, 62.4 into a 40ft, and 69.0 into a 40 HC. Awkward or cube-shaped cartons fill less.
Why is my CBM total not the same as container capacity?
CBM is the volume of your boxes as if they were poured in like liquid. Real boxes leave gaps — orientation limits, tiling remainders, the door column and stacking rules all lose space. So a shipment of 60 CBM does not fit a "67 CBM" 40ft cleanly; you need to plan the actual layout, not just compare totals.
Does CBM decide my freight cost?
Partly. Carriers bill on the greater of actual weight and volumetric weight. For sea LCL the common rule is 1 CBM = 1,000 kg, so light, bulky cargo is charged on CBM. Dense cargo is charged on weight instead. Calculate both and see which one is larger.
Who: Written and reviewed by the Kubova team, who build and operate the packing engine described here.
How: Drafted with AI assistance for research and structure; the technical claims, examples and product details are owned and verified by the team.
Why: To help logistics and engineering teams decide whether to let an AI agent plan their loads — not to chase a keyword. Published 2026-06-17.