A standard 20ft general-purpose container holds approximately 33.2 cubic metres (CBM) of usable cargo space. To calculate how many cartons fit, multiply each carton's length × width × height to get its CBM, multiply by the number of cartons for total CBM, then divide by 33.2. If the result exceeds 1.0 (100%), you need a larger container — typically a 40ft GP (67.6 CBM) or 40ft HC (76.4 CBM).
The Quick Answer: How to Calculate Carton Fit in a 20ft Container
There are two reliable methods for working out how many cartons fit in a 20ft container. Use both, then take the more conservative estimate.
Method 1: CBM Method (Recommended)
This method uses volume alone and accounts for stacking efficiency:
- Calculate the CBM of one carton: L(cm) × W(cm) × H(cm) ÷ 1,000,000
- Multiply by your total carton quantity to get total cargo CBM
- Divide by the container's usable CBM (33.2 for a 20GP)
- If the result is ≤ 1.0, your cargo fits
Worked example: You have 500 cartons measuring 60 × 40 × 40 cm each.
- CBM per carton: 60 × 40 × 40 ÷ 1,000,000 = 0.096 CBM
- Total cargo CBM: 0.096 × 500 = 48 CBM
- Utilisation in a 20ft: 48 ÷ 33.2 = 144% — it doesn't fit
- Utilisation in a 40ft GP: 48 ÷ 67.6 = 71% — a 40ft works
Method 2: Unit Count Method (Floor Area × Stack Height)
This is useful when cartons must stand on their base and cannot be mixed-stacked:
- Divide the container floor area by the carton footprint to get cartons per layer
- Multiply by the number of stackable layers (container internal height ÷ carton height)
A 20ft container has an internal floor area of roughly 5.9 m × 2.35 m = 13.87 m². A 60×40 cm carton footprint is 0.24 m². That gives 57 cartons per layer. With a 40 cm carton height and a 2.39 m internal container height, you can stack 5 layers (5 × 40 = 200 cm, leaving 39 cm unused). Total: 57 × 5 = 285 cartons — far fewer than the 500 in our example, confirming you need a bigger box.
Container Dimensions and Usable CBM Reference
Carriers publish gross CBM figures, but the usable volume is always lower due to the container structure and packing constraints. Use these figures when planning loads:
| Container Type | Internal L × W × H | Gross CBM | Usable CBM (≈85%) | Max Payload |
|---|---|---|---|---|
| 20ft General Purpose (20GP) | 5.90 m × 2.35 m × 2.39 m | 33.1 m³ | 33.2 m³ | 28,230 kg |
| 40ft General Purpose (40GP) | 12.03 m × 2.35 m × 2.39 m | 67.5 m³ | 67.6 m³ | 26,730 kg |
| 40ft High Cube (40HC) | 12.03 m × 2.35 m × 2.69 m | 76.0 m³ | 76.4 m³ | 26,480 kg |
| 45ft High Cube (45HC) | 13.56 m × 2.35 m × 2.69 m | 85.7 m³ | 86.1 m³ | 27,700 kg |
Note: Usable CBM and payload vary slightly by shipping line and container manufacturer. Always confirm with your freight forwarder.
Why "Usable CBM" Is Less Than "Gross CBM"
The gross CBM of a container is the raw mathematical volume of its interior. But you will never fill 100% of that space in practice. Here is why:
- Packing efficiency factor (~85%): Cartons are rectangular but rarely stack to a perfect cube. Gaps appear at the top, sides, and between rows.
- Odd-shaped cargo: If your cartons are not a uniform size, wasted space increases dramatically.
- Dunnage and bracing: Blocking materials, airbags, and wooden bracing boards consume 1–3% of volume.
- Forklift access: If the container is stuffed with a forklift (rather than hand-loaded), the operator needs clearance space, reducing effective depth by 20–30 cm.
- Weight limits reached before volume limits: Dense cargo such as tiles or machinery may hit the payload limit at only 50–60% of the container's volume.
As a rule of thumb, plan for 85% utilisation of the gross CBM figure when building your load plan. If your total cargo CBM divided by the container's gross CBM exceeds 85%, you risk a mis-declaration or an inability to close the container doors.
Common Carton Size Reference — CBM Quick Table
These are the ten most common export carton sizes used in Chinese manufacturing and e-commerce exports. Use this as a quick reference before running your full calculation.
| Carton Size (cm) L×W×H | CBM per Carton | Cartons per 20GP (85% util.) | Cartons per 40GP (85% util.) |
|---|---|---|---|
| 30 × 20 × 20 | 0.012 | 2,353 | 4,793 |
| 40 × 30 × 25 | 0.030 | 941 | 1,917 |
| 40 × 35 × 30 | 0.042 | 672 | 1,369 |
| 50 × 40 × 30 | 0.060 | 470 | 958 |
| 50 × 40 × 40 | 0.080 | 353 | 719 |
| 60 × 40 × 40 | 0.096 | 294 | 599 |
| 60 × 50 × 50 | 0.150 | 188 | 383 |
| 70 × 50 × 50 | 0.175 | 161 | 328 |
| 80 × 60 × 60 | 0.288 | 98 | 199 |
| 100 × 80 × 80 | 0.640 | 44 | 90 |
Should I Use a 20ft or 40ft Container? — Cost Analysis
The decision isn't purely about whether your cargo physically fits. Here's a practical cost framework:
When a 20ft Makes Sense
- Your total cargo CBM is between 15–33 m³ (50–100% utilisation of a 20GP)
- Your cargo is dense (heavy but not bulky) — you'll hit the weight limit well before the volume limit
- You ship from a port where 40ft containers carry a significant premium
- Your buyer's site has restricted access that limits container length
When a 40ft or 40HC Makes Sense
- Your cargo exceeds 33 m³ — you have no choice
- Your cargo is light and bulky (e.g., furniture, foam, plastic parts) — a 40HC's extra height (2.69 m vs 2.39 m) gives you an extra 9 m³
- The freight rate difference between a 20GP and 40GP is less than 2× (common on major trade lanes)
- You have enough cargo to split across two 20ft containers, but a single 40ft is cheaper
Rule of Thumb on Pricing
On most China–Europe and China–USA trade lanes, a 40GP costs approximately 1.5–1.7× the price of a 20GP. This means if your cargo fills more than 60–70% of a 20GP, using a 40GP for the same cost-per-CBM is actually cheaper. Always ask your freight forwarder for both quotes before booking.
Frequently Asked Questions
How many standard cartons fit in a 20ft container?
It depends entirely on carton size. A 20ft container holds 33.2 m³ of usable space. Divide your carton's CBM into 28.2 m³ (33.2 × 85% packing efficiency) to get a realistic count. For 60×40×40 cm cartons (0.096 CBM each), that's approximately 294 cartons.
Can I mix carton sizes in a container?
Yes. Calculate the total CBM of all SKUs combined and compare it to the container's usable CBM. As long as the total is under 33.2 m³ for a 20GP (and the total weight is under 28,230 kg), the shipment should fit. Ask your freight forwarder or logistics team to confirm the load plan.
What is the maximum weight for a 20ft container?
The standard maximum payload for a 20GP container is approximately 28,230 kg (28.23 tonnes). Note that the gross weight limit (tare + cargo) is 30,480 kg. Always confirm with the shipping line, as limits vary slightly between carriers and container manufacturers.
How does container utilisation affect my freight rate?
If you're shipping FCL (Full Container Load), you pay a flat rate for the container regardless of how much you fill it — so higher utilisation means a lower cost per unit. For LCL (Less than Container Load), you pay per CBM, so the calculation is more direct.
What if my cargo exceeds a 20ft but doesn't fill a 40ft?
This is the most common dilemma in container planning. Compare the FCL rate for a 40GP against the LCL rate for the overflow cargo. In many cases, booking a 40GP and accepting lower utilisation is still cheaper than an LCL shipment — especially for time-sensitive cargo where LCL transit times are longer.
Ready to calculate your exact container fit? Enter your carton dimensions and quantities into our free tool and get an instant utilisation result. Use our Container Load Calculator to get the exact count for your cargo →