Choosing a container size sounds like a simple question about volume. In practice it is a question about three things at once: how much you need to store, how much space you have to put the container in, and how you intend to get things in and out of it. Buy on volume alone and you will end up with a unit that is either too tight to work in or too big to get onto site. This guide compares the sizes commonly available in the UK and gives a practical way to choose between them.
The standard sizes at a glance
Every ISO shipping container is 8ft (2.44m) wide externally. Standard height is 8ft 6in (2.59m); a high cube is 9ft 6in (2.90m). Length is what varies, and internal dimensions are always a little smaller than external because of the corrugated steel walls.
- 8ft container — roughly 2.44m long externally. Internal floor area around 4.5 square metres, about 10 cubic metres of space. Fits on a small driveway or in a garden.
- 10ft container — roughly 3.0m long. Around 6.5 square metres of floor, about 16 cubic metres. The smallest size most UK depots stock in quantity.
- 20ft container — 6.06m long externally, about 5.9m internally. Around 13.8 square metres of floor and roughly 33 cubic metres. Empty weight about 2.2 tonnes.
- 40ft container — 12.19m long externally, about 12.0m internally. Around 28 square metres of floor and roughly 67 cubic metres. Empty weight about 3.7 tonnes.
- 40ft high cube — same footprint as a 40ft, with an extra foot of internal height (about 2.69m clear). Roughly 76 cubic metres.
- 45ft high cube — 13.72m long. Specialist sizes; less common and harder to place.
Two useful rules of thumb: a 40ft container gives you almost exactly twice the space of a 20ft, and a high cube gives you roughly 13% more volume than a standard unit of the same length for a modest price difference.
What actually fits
Volume figures are hard to picture. Rough, real-world comparisons help more:
- 8ft or 10ft — garden equipment, a motorbike, bicycles, tools, a market stall’s stock, the contents of a small flat. Good for allotments, gardens and tight yards.
- 20ft — the contents of a typical three-bedroom house with room to spare, a small car plus tools, a builder’s plant and materials for a job, pallet racking down one wall with a working aisle. This is the UK’s default size for a reason.
- 40ft — the contents of a large house, roughly 20–22 standard UK pallets on the floor, a full workshop, or a vehicle plus substantial storage.
- High cube — anything where you need headroom: racking three or four levels high, working inside the unit standing up comfortably, storing a tall vehicle, or converting to a room where floor and ceiling insulation will eat 150mm of height.
The three questions that actually decide it
1. Can it physically get to your site?
This eliminates more 40ft containers than anything else. A 40ft unit arrives on an articulated lorry that is around 16m long overall and needs a wide sweep to turn in. Tilt-bed delivery of a 40ft needs roughly 30m of straight, level run. Many farm entrances, most residential driveways and a lot of urban yards simply cannot take it, and the answer is two 20ft containers rather than one 40ft.
Two 20ft units also give you flexibility a 40ft cannot: you can put them in different places, sell one later, and you get twice as many door ends. The trade-off is a slightly higher cost per cubic metre. Read our guide to delivery access and offloading before you decide.
2. How will you get things in and out?
A standard container has doors at one end only. In a 40ft unit, anything at the far end is 12 metres from the door, which is fine for long-term storage and infuriating for anything you need weekly. If you want regular access to everything, a 20ft is easier to work in, or look at units with additional access: open side containers with full side access, double-door units with doors at both ends, or open top containers where loading happens from above.
Also think about the approach. Getting a pallet truck or forklift into a container needs a ramp or a raised, level platform at the door end, and enough hard standing outside to manoeuvre on.
3. What is the container for beyond storage?
If you are converting the unit, height and length behave differently. A 20ft high cube converts into a comfortable single office or garden room. A 40ft high cube gives you enough length for two rooms plus a corridor. Once insulation, boarding and flooring are in, a standard-height container feels noticeably low, which is why almost all conversions start with a high cube. Our modified containers and cabins are worth comparing against a self-build before you commit.
Sizing it honestly
A method that works: measure or estimate the footprint of what you are storing, add 30% for aisles and stacking inefficiency, and then check the result against the door-end access you need. Do not size to the absolute limit — a container packed wall to wall is a container you cannot use without unpacking half of it.
The most common sizing mistake is buying too small to save a few hundred pounds, then needing a second unit within a year. The second most common is buying a 40ft for the cost-per-cubic-metre saving and discovering the lorry cannot reach the intended spot. Both are avoidable with a tape measure and a walk around the site.
Cost per cubic metre is not the whole story
A 40ft container is cheaper per cubic metre than a 20ft, and a high cube is cheaper per cubic metre than a standard. But the cheapest space is only good value if you can deliver it, place it, and reach into it. Factor in delivery, whether you need a crane, the ground preparation for a longer unit (a 40ft needs six bearing points, not four, to avoid sagging in the middle), and whether planning constraints on your site favour something less conspicuous.
Still not sure?
Tell us what you are storing, where the container is going and how you will access it, and we will tell you which size makes sense — including when a smaller or cheaper unit will do the job perfectly well. Start with our Buyer’s Guide for the full picture, check the Condition Guide to choose a grade, or browse storage containers, shipping containers and high cube containers currently in stock.
Once you have settled on a size, check it against your access in our guide to delivery, craning and ground preparation, confirm whether you need planning permission, and see the regional notes under delivery areas.
Request a delivered price and we will quote the container and its grade as a single figure, delivered free to your postcode.