How to Measure Shipping Container Dimensions Correctly

What size shipping container do you need? Conveniently, the shipping industry categorises containers by size, so there’s no need to learn new terms when purchasing your unit – you just need to convert from imperial to metric.

The most common options are 20ft and 40ft, and for the most part they do what they say on the tin: 20 footers are 6.06m (20ft) long, 40 footers are 12.19m (40ft) long.

But there is some nuance to these numbers that container buyers need to be aware of. Misunderstanding shipping container dimensions, or not measuring them properly, can lead to a number of issues: from failed deliveries, to rejected council permits, to equipment not fitting.

This isn’t an article on how to use a tape measure. It’s a guide to how the dimensions of a container dictate the success of your project, and how to ensure you measure correctly and choose your container size wisely.

External vs internal shipping container dimensions

First things first: when we talk about ‘20ft’ and ‘40ft’ containers (or less common 8/10/48ft containers), we’re referring to the external length of the unit.

The external dimensions of containers are set out by global shipping standards. These enable the uniform infrastructure that ensures containers can be easily transported on road, rail and sea across the world.

If you’re looking to store goods on your property or undertake a container conversion project, you’ll need to know the internal dimensions too. The structural steel elements – corrugated walls, corner posts, beams, flooring – mean that inside the container you typically lose:

• ~150mm of length
• ~100mm of width
• ~200mm of height

Take a standard 20ft shipping container:

(For a complete rundown of container dimensions, check out our comprehensive guide.)

This is a crucial difference for anyone looking to use the container to store large items, or planning the layout of a site office, sales kiosk or tiny home conversion. Those missing millimetres can be the difference between a machine, bed or desk fitting snugly or not fitting at all.

Shipping container door measurements

It’s not just a matter of whether large items fit within the container’s footprint – perhaps more importantly, it’s whether they fit through the door.

Container door openings are slightly smaller again than the internal width and height dimensions: 3mm narrower and 110mm shorter on standard 20ft and 40ft containers.

You may be able to tilt or twist items to squeeze them inside, but this can be tricky if the item is particularly heavy. It’s far wiser to only load items that are smaller than the door opening.

Theoretical vs usable volume

To calculate the volume of a container, you simply multiply the internal length, width and height dimensions together. But this theoretical volume isn’t quite the same as the actual usable volume, which is compromised ever so slightly by:

• Corner castings: While they don’t impact floorspace, these heavy steel blocks do take up ~150mm of room in the top corners, so can affect the storage of tall items and the installation of cabinetry.
• Lashing rings: Internal tie-down points have the potential to snag wide loads, but they are usually positioned within wall corrugations, so shouldn’t impact total volume in any meaningful way.

High cube containers offer an effective way to secure extra volume without expanding the footprint of the container. 305mm taller than standard, they add 300mm of internal height for you to use.

Common measurement pitfalls to avoid

There are a few common mistakes that first-time container buyers can make when trying to figure out the right container size for their needs or project. Avoiding them can ensure you don’t lose money on an unsuitable investment.

• Measuring the outside: It’s a basic one, but worth still repeating: always base your purchase decision on the internal dimensions, not the external.
• Not accounting for floor height: While shipping containers come with basic plywood or bamboo flooring, you may want to add your own finish, which will ever so slightly affect internal height.
• Inward creep from insulation: If you’re planning a living or working space, you’ll need this big metal box to be insulated, which will eat into the internal volume.
• Drop-off and door opening: In terms of placement, you need to account for the room a truck will need to unload your container, and the fact that standard doors swing out 270॰, risking collision with anything (fences, machinery, other containers) in that arc.

Find your perfect container today

Not sure what the perfect container is for your situation? Want to gain a deeper understanding of how to measure containers accurately, and how to choose the right unit? We’re here to help.

At Shipping-containers.com.au we’re a 100% independent platform designed to guide you to your perfect shipping container size. Once you’ve locked that in, we then connect you with local, vetted suppliers and modification partners who can deliver.

Start your shipping container journey today