How Many Units Fit in a Shipping Container? How to Size Your Order to the Freight

How many units fit in a shipping container?

There is no single answer, because containers are sold by space and products are sold by unit. What decides it is your export carton: its outside dimensions, and how many units sit inside it.

The short version. A 20ft container holds about 25 to 28 cubic metres of packed cartons. A 40ft holds 54 to 58. A 40ft high cube holds 60 to 68. Divide packed capacity by the cubic metres of one carton, round down, then multiply by units per carton. That number is your container.

For a mid-sized homewares carton at 48 by 32 by 30 centimetres holding 12 units, a 20ft takes about 588 cartons, or 7,056 units. Change that carton by two centimetres and you lose a thousand of them. Below is the maths, and the places founders lose capacity without knowing it.

If you are still choosing between shared and full container, start with LCL vs FCL. This piece assumes you are filling one.

What are the real internal dimensions?

Quoted container sizes are the outside. Cargo goes inside. Use these.

• 20ft standard. 5.90 by 2.35 by 2.39 m. 33.2 CBM theoretical. 25 to 28 CBM packed.
• 40ft standard. 12.03 by 2.35 by 2.39 m. 67.7 CBM theoretical. 54 to 58 CBM packed.
• 40ft high cube. 12.03 by 2.35 by 2.69 m. 76.3 CBM theoretical. 60 to 68 CBM packed.

The gap between theoretical and packed is not padding. It is the top layer you cannot safely stack, the strip of floor your carton does not divide into, and the room loaders need to work. Plan on packed. Anyone quoting you the theoretical figure has not loaded a container.

Two more numbers worth having. The door opening on a 20ft is about 2.34 m wide and 2.28 m high, lower than the internal height, which matters for tall palletised loads. And a 40ft high cube gives you 30 cm of extra height, not extra floor. High cube helps bulky light product. It does nothing for anything heavy.

How do you work out cartons per container?

Not by dividing CBM. That gives you a ceiling, not a count. Cartons are boxes, and boxes do not flow like liquid.

Work it in three steps. Cartons along the length: container length divided by one carton dimension, rounded down. Cartons across the width: container width divided by the other carton dimension, rounded down. Layers: internal height divided by carton height, rounded down, then take a layer off unless the carton is rated to stack that high.

Multiply the three. Then run it again with the carton rotated ninety degrees and keep whichever count is higher. Loaders mix orientations to claw back the last row, but your plan should not depend on it.

Two rules the arithmetic hides. Round down every time, because a carton 3 mm too wide costs you the whole row. And use export carton dimensions, never the retail box and never the product. Factories quote product dimensions by default, and the export carton is usually 4 to 8 per cent larger than the sum of what is in it. If you are still developing your packaging, the carton is part of that spec.

A worked example: 7,056 units in a 20ft

Illustrative numbers, but this is the method we run on client orders.

Product, a boxed ceramic vase. Export carton 48 by 32 by 30 cm, 12 units per carton, gross weight 11 kg. CBM per carton: 0.48 x 0.32 x 0.30 = 0.046 CBM.

• Along the length. 5.90 divided by 0.48 = 12 cartons.
• Across the width. 2.35 divided by 0.32 = 7 cartons.
• Per layer. 84 cartons.
• Layers. 2.39 divided by 0.30 = 7 layers, so 2.10 m loaded with 29 cm spare at the top.
• Total cartons. 588.
• Volume check. 588 x 0.046 = 27.0 CBM, inside the 25 to 28 band, so the plan is real.
• Weight check. 588 x 11 = 6,468 kg, nowhere near the limit.
• Units. 588 x 12 = 7,056 units.

That is the order quantity. Not 7,000. Not 5,000. 7,056.

Look at step two again. Seven cartons across uses 2.24 m of a 2.35 m width. Eleven centimetres of floor runs the full length of the container, unused, and there is nothing you can do about it at this carton size. Which brings us to the part nobody mentions.

Why two centimetres of carton width costs you a thousand units

Same product. The factory revises the carton to 48 by 34 by 30 cm for a thicker insert.

Across the width: 2.35 divided by 0.34 = 6 cartons, not 7. Per layer, 72. Total, 504 cartons. Units, 6,048.

Two centimetres of carton width cost 1,008 units. Fourteen per cent of the container, for exactly the same freight bill.

Run it into unit cost. An all-in 20ft from South China to Melbourne at, say, $3,200 is 45 cents a unit across 7,056 units. Across 6,048 it is 53 cents. Small on its own. Not small across four reorders a year, and not small when you find out after the space is booked.

Two things follow. Ask for the carton dimension sheet before you approve the sample, not after. And write the carton dimensions into the purchase order with the same weight as the product spec, so a change needs your sign-off. A factory that revises a carton is not doing anything wrong. They simply do not know your container plan.

Will weight or volume run out first?

Divide payload by packed volume and you get the cargo density at which a container fills by weight instead of space.

• 20ft. About 28,000 kg over 28 CBM, so roughly 1,000 kg per cubic metre.
• 40ft high cube. About 26,300 kg over 68 CBM, so roughly 390 kg per cubic metre.

Anything denser than about 390 kg per cubic metre hits the weight limit in a 40ft high cube before it fills the space. Tiles, stone, ceramics, liquids, anything with a steel frame. Heavy product belongs in a 20ft, where you have a tonne of payload for every cubic metre. Bulky light product belongs in a 40ft high cube.

One Australian caveat. The container is rated to around 28 tonnes. Your carrier may not take it. Road operators here often cap a loaded 20ft well below the rating for standard haulage, and a heavy container can need a different trailer or a permit. Ask your forwarder what the road limit is to your delivery address before you plan to load to the ceiling.

Pallets or floor loaded?

Floor loaded means cartons stacked by hand, wall to wall. Palletised means cartons on pallets, moved by forklift.

Floor loading wins on volume. You get the 588 cartons. Palletising costs you the pallet height, the overhang you cannot use and the gaps between pallets. On a standard Australian pallet at 1165 by 1165 mm you fit 10 pallets in a 20ft and 20 to 21 in a 40ft, single layer, and you typically give up 12 to 18 per cent of usable volume.

Floor loading loses on labour. Someone unloads 588 cartons by hand at your end. Australian third party warehouses charge for that, usually as a destuffing or hand unload fee, and it can run several hundred dollars a container. Get the number before you decide. On light, high value product, floor loading still wins. On heavy cartons, or where your warehouse bills by the hour, pallets often win once you count the unload.

There is a third option worth asking for. Floor loaded from the factory, palletised at an Australian depot. It costs a handling fee and buys you the volume.

What to ask the factory before you plan a container

Send this list and wait for the answers before you book freight.

1. Export carton dimensions in centimetres, outside measurements, length by width by height.
2. Units per carton.
3. Net and gross weight per carton.
4. CBM per carton, so you can check their maths against yours.
5. Total cartons and total CBM at the order quantity you are considering.
6. Whether the carton is rated for stacking, and to how many layers.
7. Whether the carton spec changes if the packaging or insert changes.
8. A loading plan and photos before the container is sealed.

Ask for the packing list in the same format you will hand your freight forwarder and your warehouse. One spreadsheet, carton by carton, with shipping marks. It saves an argument at both ends.

How do you size a reorder to the container?

Founders order round numbers. Containers do not care about round numbers.

Work backwards instead. Take packed container capacity in units, then ask whether you can sell it. If a 20ft is 7,056 units and 7,056 is more than you can move this season, you have a real choice between shipping a part container and holding cash. That is not a freight decision. It is a stock and cash decision, and Kristy covers it properly in how much stock to order for your first product run.

What freight can tell you is the price of each option, per unit, before you commit. Get both numbers from your forwarder: the LCL rate at your actual CBM, and the all-in FCL rate. Add destination charges to each, because they do not scale the same way. Then choose.

One timing note. Container space out of China tightens either side of Golden Week and hard before Chinese New Year. If you are sizing an order now for a first quarter arrival, book space earlier than feels necessary.

Where this fits in your unit cost

Container maths sits between your factory quote and your landed cost. Get the carton right and freight per unit falls without renegotiating a thing. Get it wrong and you pay full container rates to ship 14 per cent air.

We size client orders to the carton before the purchase order goes out, not after the freight quote comes back. If you are already importing and want someone to check your carton spec against a container before the next order, email kristy@sourcehaus.co. We are in China in October for Canton Fair Phases Two and Three if you would rather do it standing on a factory floor.