A square box will have an outer perimeter and a smaller inner perimeter. A cylindrical box will have an outer and inner circumference.

Are there common words or technical terms for an inner perimeter and/or circumference?

This presumes that a "perimeter" or "circumference" is typically assumed to be outer, which is my impression.

  • 3
    Is there a common word or technical term for an "inner circumference"? No.
    – Greybeard
    Commented Dec 31, 2021 at 16:11
  • 4
    'Outer circumference' and 'inner circumference' are technical terms, often used for say cylindrical tanks and discs (eg washers). Commented Dec 31, 2021 at 16:30
  • Your question isn't clear, because "circumference" is usually a property of circles, which are two-dimensional (unlikes boxes) and have no straight edges (also unlike boxes). Please clarify what you mean. Commented Dec 26, 2022 at 19:41
  • Are you referring to the two circles that can be drawn within the walls of a box and around the corners of a box?
    – Elliot
    Commented Dec 27, 2022 at 3:34
  • 1
    Apologies – I did not realise "circumference" would not be appropriate for a square box, but that makes sense, of course. Now hopefully clarified.
    – Henrik N
    Commented Dec 30, 2022 at 12:02

2 Answers 2


Is there a term for "inner circumference"?

Only on circular objects.

Otherwise, it is an "internal perimeter" which, as we will see, is a useless measurement.

Assume a box of exterior dimensions 20cm height, 41cm width and 32cm depth that has, for example, internal dimensions of 19cm height, 40cm width and 30cm depth.

This has

three external perimeters = 2(width + height) = 122cm; 2(height + depth) = 104cm , and 2(width + depth) = 146cm and


three internal perimeters = 2(width + height) = 118cm; 2(height + depth) = 100cm, and 2(width + depth) = 142cm.

You will now note that of the 6 perimeters, no two are the same.

You will also note that, for a general box, it is uncertain which side is the top, bottom, or side

For these reason, there is no easy solution to your description.

The effect of this is that as a general concept what you are asking must be described as a clause.

Even in a specific case, where the orientation of the box is known, it may be possible to describe the internal and external (width + depth) measurement as “the horizontal perimeter” but this leaves the two dimensions that include height as undescribed and indescribable in a short phrase.

Out of interest, do you have specific terms in your language?

  • 1
    I didn't notice any indication that the OP is familiar with a language other than English... Commented Dec 1, 2021 at 16:16
  • 1
    I think you are assuming that the box in question is a cardboard carton or something similar. The inner circumferemce of a small box made from thick wood (for instance) would be considerably smaller, proportionally, than its outside circumference.
    – BoldBen
    Commented Dec 2, 2021 at 1:31
  • @BoldBen With the words "assume" and "for example", it should be obvious that the actual measurements can be anything at all - as long as each exterior dimension is greater than its equivalent interior.
    – Greybeard
    Commented Dec 2, 2021 at 9:57
  • Fair enough with circumference only applying to a cylindrical box. Now clarified in the question. Regarding the ambiguity of exactly which sides one is referring to, I don't see that as a problem – it could be the case that there are terms for some of those, or some broader term that would apply to all of them.
    – Henrik N
    Commented Dec 30, 2022 at 12:06
  • 1
    On the broad question, we do use "internal dimensions/measurements."
    – Greybeard
    Commented Dec 30, 2022 at 13:27

This may not be what the questioner means, but should be said: Geometric shapes are defined by line segments that have no "thickness" or any dimension other than length. The question assumes that the "inside" perimeter and the "outside" perimeter of a box (rectangle) or the inside and outside circumference of a circle are not the same. In fact, mathematically, they are the same.

Of course, for physical objects with actual walls, the inside and outside measurements are different. But these are not the same as "perimeter" and "circumference", which are mathematical terms with precise definitions.

If you are looking for what to call these actual measurements, "inside" and "outside" measurements or dimensions are clear enough.

  • Good distinction. I meant for real-world shapes.
    – Henrik N
    Commented Jan 25 at 8:44

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