What a 36 Square Metre Insulated Container Actually Means
Short answer: it probably is not a container measurement at all. No standard shipping container has an internal lining area of 36 square metres. A 20ft container presents roughly 53 square metres when you line the walls and ceiling, and about 67 square metres if you include the floor. A 40ft is closer to 97 and 125. If you have been quoted 36 square metres, it is measuring something else.
That matters, because container insulation is priced and specified on surface area. Get the number wrong and you order the wrong quantity of material, budget the wrong amount, or compare two quotes that are not measuring the same thing.
Here is what the real figures are, where a number like 36 comes from, and how to work out your own.
Why is container insulation measured in surface area rather than floor area?
Most container specifications you encounter are about volume or floor space. How many pallets fit. How many cubic metres. How many square metres of floor.
A thermal liner is different. It sits against the internal surfaces of the container, so what you are buying is the area of those surfaces. That is walls, ceiling and sometimes floor, not the area of the ground the cargo stands on.
The single most common source of confusion in quoting comes from this distinction. A 40ft container has about 28 square metres of floor. Lining it takes closer to 97 square metres of material. Those two numbers differ by a factor of more than three, and quoting the first when you mean the second produces a figure that is badly wrong in a direction nobody notices until the material arrives.
What are the real internal surface areas?
The figures below are calculated from standard internal dimensions. Figures are approximate, because corrugation profiles vary slightly between manufacturers and because door frames and posts take up a little of the usable surface.
Five-sided means four walls plus the ceiling. Six-sided adds the floor. Those are the two specifications you will be quoted on most often, and the difference between them is substantial: on a 40ft it is roughly 28 square metres of additional material.
Calculated from standard ISO internal dimensions of 12.02m by 2.35m by 2.39m. Source: standard ISO container specifications. Figures approximate, corrugation and door framing vary.
So where does a figure like 36 square metres come from?
We cannot tell you with certainty what any particular quote refers to, but there are three plausible explanations and it is worth checking which applies.
It is a partial coverage specification.
Not every job lines the whole container. If you are lining two side walls only on a 20ft, that is about 28 square metres. Add one end wall and you are at roughly 34. Four walls with no ceiling and no floor comes to about 39. A figure in the mid-thirties sits in that range, so it may well be a partial specification rather than a full one.
It is a floor area, not a lining area.
Some modular and converted container products are sold by internal floor space in the way a room would be. A 36 square metre insulated unit described that way is a building measurement, roughly the footprint of two and a half 20ft containers placed side by side. That is a different product from a lined shipping container and it is not what we supply.
It is a material quantity rather than a container specification.
Liner material is manufactured and sold in defined widths and lengths. A quantity of 36 square metres might simply be what was ordered for a particular job, including offcut allowance, rather than a description of the container itself.
If you have that figure in front of you, the useful question to ask whoever supplied it is a simple one: is this the area of material, or the area of container being covered, and which surfaces are included?
How does coverage choice change the number?
The specification decision gets made here, and it is worth understanding before comparing quotes.
Walls and ceiling, five-sided, is the standard specification for most ambient cargo. It addresses the surfaces where the majority of heat transfer and condensation occurs, because the roof takes direct solar load and the side walls take the largest area of ambient exposure.
Six-sided, including the floor, adds material and cost. It is worth specifying where the floor is a genuine heat path, or where cargo sits directly on the deck rather than on pallets.
Partial coverage applies to specific surfaces only, where the risk is concentrated. Read our detailed guide to five-sided, six-sided and partial lining to decide which specification your route and cargo need.
Why does the number matter commercially?
Three reasons, and they compound.
Material. Surface area determines how much liner is required. It is the primary input to the quantity, so an incorrect area produces an incorrect order.
Fitting time. More area takes longer to fit. Our prefabricated Integrated Liner goes into a container in roughly 7 to 20 minutes depending on size, while the Roll Liner is cut and fitted on site and takes 20 to 45 minutes. Coverage specification moves you within those ranges. Full details of both options are on our thermal container liner installation service page.
Comparison. If you are comparing suppliers, area and coverage are the two variables that make quotes comparable or not. A cheaper quote covering four walls is not cheaper than a quote covering five surfaces. It is a different job. Our guide to the cost to insulate a shipping container breaks down how those comparisons actually work.
How do I work out the area for my own containers?
If you want to calculate it rather than look it up, the arithmetic is straightforward.
Side walls: internal length multiplied by internal height, multiplied by two. End walls: internal width multiplied by internal height, multiplied by two. Ceiling: internal length multiplied by internal width. Floor: the same as the ceiling, added only if you are specifying six-sided.
Add the surfaces you intend to cover. Allow a margin for corrugation, door framing and fitting overlap rather than working to the exact figure.
If you would rather not do the arithmetic, our container insulation calculator takes your container size and route and returns an indicative comparison.
What this does not tell you
Surface area tells you how much material a job needs. It does not tell you whether your cargo needs insulating at all, and that is the more important question.
A thermal liner suits ambient cargo that does not technically require a reefer, but where the container getting hot, cold or damp still causes expensive damage or rejection. It is not the answer for frozen cargo, fresh meat and fish, produce needing controlled atmosphere, or anything on a validated cold chain. Those need active refrigeration and we would tell you so.
We have been supplying and installing container liners since 1989, and the area calculation is usually the last question rather than the first. The first is whether the cargo, the route and the season justify lining the container in the first place.
Getting an accurate figure for your containers
Tell us the container size, what you are shipping and which lane it runs on, and we will confirm the coverage specification and the area it requires. If the answer is that your cargo does not need a liner, we will tell you that too.
