The ISO 668:2013 international standard defines dimensions and rated mass limits for "series 1" freight containers.

ISO 668 defines the following dimensions:

- Nominal lengths include 10, 20, 30, 40 and 45 feet.
- Uniform width of 8' (2.44m).
- Recognised heights include 8' (2.44m), 8'6" (2.59m) and 9'6" (2.9m).

Today, a typical container is 8'6" high while a high box (often called a high cube or HC) is 9'6".

The length of 40 feet (12.19 m) is considered the starting basis for shorter nominal container lengths. Containers with shorter nominal lengths of 10', 20' or 30' are actually 1.5 inches shorter than their indicated length so that when combining any two of them the total length is exactly 40' with a 3 inch gap in-between. A 20' container is actually 19'10,5" (6.06 m) long.

The capacity of a container is usually expressed in units of twenty feet. Known as Twenty-foot Equivalent Units (or with the acronym TEU), one equivalent unit is equal to the capacity of a single 20' by 8' container. As this is an approximate measure, the height of the box is not considered.

Likewise, 40' and 45 containers are both commonly considered two TEU. Two TEU are equivalent to one FEU (Forty-foot Equivalent Unit).

48' (14.63m) and 53' (16.15m) containers are both used in North America. They are high cube containers being 9'6" (2.9m) in height. They are also wider than ISO containers at 8'6" (2.59m).

The term "mass" is often used instead of weight. Tare weight refers to the weight of the container while net weight refers to the weight of the contents, or "payload".

**Gross Weight = Tare Weight + Net Weight**

The maximum permissible gross weight for a 20' container is 24,000kg. For 40' containers, this extends to 30,480kg.

The maximum permissible net weight for 20' and 40' containers is about 22,000kg and 27,000kg respectively.

Note: the legal limits for container weights vary by country. Rated limits should not be confused with legal limits.