How to Measure Shipping Container Dimensions Correctly (Internal vs External)

What size shipping container do you need? The container industry makes that part easy: units are named by their external length, so a 20ft container is 20 feet long and a 40ft container is 40 feet long. Simple enough, until you try to fit a specific machine, a bed or a pallet layout inside and discover the numbers do not mean what you assumed.

Misreading container dimensions causes real problems: equipment that does not fit through the door, a layout that does not work, a delivery truck that cannot get in, or a permit application with the wrong footprint. This is not a guide to using a tape measure. It is a guide to which numbers matter for your project, and how to read them so you choose the right size the first time.

External vs internal shipping container dimensions

When people say 20ft or 40ft (or the less common 8ft, 10ft and 45ft), they mean the external length. Those external dimensions are fixed by ISO standards so that every container fits the same trucks, railcars, ships and cranes worldwide.

If you plan to store goods, set up a site office or run a conversion project, you need the internal dimensions. The corrugated steel walls, corner posts, top and bottom rails and the floor all take up space. In a standard container you typically lose:

• about 6 inches (160 mm) of length
• about 4 inches (100 mm) of width
• about 8 inches (200 mm) of height

Here is a standard 20ft container:

For every size side by side, see the shipping container dimensions guide.

That difference matters when you are storing large items or planning the layout of a 20ft container office, kiosk or tiny home. A few inches decide whether a machine, a bed or a desk fits along the wall or does not.

Shipping container door measurements
Fitting inside the footprint is one thing. Fitting through the door is what actually matters when you load. The door opening is slightly smaller than the internal cross section: on standard 20ft and 40ft containers it is about 7 ft 8 in wide and 7 ft 6 in high (2,335 x 2,280 mm), roughly 4 inches lower than the internal height.

You can sometimes tilt or angle an item to get it through, but with heavy items that is risky. Plan for items that are smaller than the door opening. If you regularly load wide or tall equipment, look at a high cube or a side opening unit instead.

Theoretical vs usable volume

Multiply the internal length, width and height and you get the theoretical volume: about 1,170 cubic feet (33 m³) for a standard 20ft. The space you can actually fill is a little less:

• Corner castings: the heavy steel blocks in the top corners take up about 6 inches (150 mm). They do not affect floor space, but they matter for tall items and for fitting cabinets or shelving at the top of the wall.
• Lashing rings: the tie-down points sit within the wall corrugations, so they rarely cost you volume, but they can snag a wide load.

If you need more room without a bigger footprint, a high cube container is the answer. It is about 12 inches (305 mm) taller externally and gives you close to a foot of extra headroom inside, roughly 12% more volume on the same floor area.

Common measurement pitfalls to avoid

First-time buyers make the same handful of mistakes. Avoiding them keeps you from paying for a container that turns out to be the wrong size.

• Measuring the outside: base your decision on the internal dimensions, not the nominal size on the listing.
• Forgetting the floor: containers come with marine plywood or bamboo flooring, usually about 1 1/8 inches (28 mm) thick. Add your own finish and you lose a little more height.
• Insulation creep: a living or working space needs insulation and lining. Two to four inches per wall is common, and it comes straight out of the internal width and length.
• Door swing and truck access: standard doors swing open 270 degrees. Leave room in that arc, and leave room for the tilt bed truck to back in and slide the container off. A side yard that fits the container may not fit the delivery.
• Road height: a high cube on a standard trailer sits close to the typical 13 ft 6 in US road clearance. If you have low bridges or overhead lines on the way in, ask your supplier about routing before you order.
• Used units: patches, floor replacements and door repairs on used containers can shift internal measurements by an inch or two. If your build is tight, measure the actual unit before you cut anything.

Find the right container size

Not sure which size fits your project? Start with the dimensions guide to compare 10ft, 20ft, 40ft and high cube side by side, then check shipping containers for sale to see what is available near you.

shipping-containers.com is an independent platform, not a dealer. Once you know your size, one request goes to vetted local suppliers across the US who respond with quotes. One request, multiple quotes, no fees.