The most common mistake in choosing a container is looking only at volume. A 40' has twice the volume of a 20' but does not carry twice the weight. With heavy cargo the limit is weight, not volume, and that limit is set by the container itself, the shipping line's rules and the road weight limits on the way to the port.
The figures below are approximate values for the standard dry containers used across the industry. There can be a few centimetres of difference depending on the manufacturer and the age of the box. Confirm exact values with the line when you book.
The 20' standard container
A 20' container measures roughly 5.90 m long, 2.35 m wide and 2.39 m high inside, for a volume of about 33 m³. Its empty weight (tare) is around 2.2 tonnes. On most models the maximum permitted gross weight is around 30 tonnes, so in theory it can take roughly 28 tonnes of cargo. In practice the line's and the route's limits come into play. This is the most used type for dense cargo such as pulses, sugar and flour. With these goods you approach the weight limit before the box is full, so little space is wasted.
The 40' standard container
A 40' container measures roughly 12.03 m long, 2.35 m wide and 2.39 m high inside, for a volume of about 67 m³. Its tare is around 3.7 tonnes. Although it has twice the volume of a 20', it carries not much more cargo; on many models the maximum payload is roughly 26-28 tonnes. That is why putting heavy cargo in a 40' rarely makes sense: half the box travels empty while the freight is charged as a 40'. The 40' comes into its own with light, bulky cargo, for example packaged dry food, furniture or bulky machine parts.
The 40' HC (high cube) container
The 40' HC has the same floor dimensions as the 40' but is about 30 cm taller. Its internal height is roughly 2.69 m and its volume about 76 m³. The extra height makes a difference with light cargo that can be stacked high. With heavy cargo it has no advantage over a standard 40', because the weight limit is in the same range. On some lines and routes the freight for a 40' and a 40' HC is very close or even identical. So when booking light cargo, it is often worth asking whether an HC is available.
Which one for pulses: sacks and big-bags
Chickpeas, lentils, beans and other pulses are dense cargo; a 20' approaches its weight limit before it is full. That is why the 20' is the most common type in pulse exports. With 25 or 50 kg sacks stacked by hand, a 20' is often loaded with around 24-26 tonnes. With one-tonne big-bags, the floor takes two rows and, stacked two high, about 20 big-bags fit. Loading big-bags is faster, but the same container takes less product than it would in sacks. The exact quantity depends on the product's density, the packaging and the weight the line allows, and is settled in the quote.
Weight limits, road haulage and VGM
What a container can carry and what you can actually load are not the same thing. Shipping lines apply weight limits on some routes or charge a surcharge for heavy boxes. The axle and gross weight limits on the road between the plant and the port also play a part. In addition, under the SOLAS rules the verified gross mass (VGM) of every container must be declared to the line before it is loaded on the vessel. If the declared weight does not reflect reality, the container may not be loaded. When you ask FM Port for a container quote, stating the product, the packaging and the target tonnage makes it easier to pick the right type.
