Free tool
Box size calculator
Give the product's dimensions and how many go in the box. This works out the internal carton size to ask for — in inches, in the right order, with clearance allowed.
Published · Updated
In short
- Internal carton size = product dimension × how many fit along it, plus clearance.
- Always ask for INTERNAL dimensions. External includes the board, which changes with ply.
- Write them length × width × height — length is the longer side of the open face, height is the depth.
- A few millimetres of clearance on each dimension suits a rigid product; allow more for soft packaging or an insert.
- The finished carton is made to a manufacturing tolerance, as all corrugated is. Ask us what ours is.
Work out the size
Measure the product at its widest, longest and tallest points, including anything that sticks out. Then say how many units sit along each direction inside the box.
Internal size to ask for
—
- Units per box
- —
- In millimetres
- —
- Internal volume
- —
Send this line with your enquiry:
—
Request a quoteThe sum, written out
Nothing is hidden in the calculator. For each of the three directions:
Then the three results are named. Height is the depth from the top opening down to the base — whichever way up the box is filled. Of the two remaining, length is the longer and width is the shorter. That is the convention this market quotes in, and it is why 18 × 12 × 10 and 12 × 18 × 10 are two different boxes.
A worked example
A product measuring 8 × 6 × 4 inches, two along the length and two across the width, one layer high, with a few millimetres of clearance:
- Length — 8 × 2 = 16 inches, + 0.2 = 16.2 in
- Width — 6 × 2 = 12 inches, + 0.2 = 12.2 in
- Height — 4 × 1 = 4 inches, + 0.2 = 4.2 in
So the enquiry says 16.2 × 12.2 × 4.2 inches internal, 4 units per box. That is a specification a supplier can quote against without a phone call.
Internal, not external
This is the mistake that costs the most, and it gets worse as ply goes up. An external measurement includes the thickness of the board on both sides of every dimension. Board thickness changes with construction — 5-ply is thicker than 3-ply, 7-ply thicker again — so the same external size gives you a different amount of room depending on what it is made from.
Ask for internal dimensions and the space your product has is fixed no matter which board the specification lands on. If you need the carton to fit inside something else — a master carton, a shelf, a pallet footprint — tell us the external limit as well and we will work back from it.
If you are packing more than one
The calculator asks how many units go in each direction rather than working it out from a total, and that is deliberate. Sixteen units is four by four by one, or two by four by two, or eight by two by one — three different boxes, with different board areas and different stacking behaviour. Only you know which arrangement suits the product.
If the units are boxed themselves and you are sizing the outer, the same sum applies to the inner packs rather than the product — and what is a master carton covers what else that box has to carry.
Common questions
Does this give internal or external dimensions?
Internal — the space inside the carton, measured to the inside faces. That is what you should send with an enquiry, and what we quote against. External dimensions include the thickness of the board, which changes with ply, so the same external size gives you less room in 5-ply than in 3-ply.
How much clearance should I allow?
Enough that the product goes in without forcing and does not rattle. A few millimetres on each dimension is usually right for a rigid product. Allow more if the item has soft packaging, a label that must not scuff, or an insert around it — and tell us what is going inside so we can allow for it properly.
What order do the dimensions go in?
Length × width × height. Length is the longer side of the open face, width is the shorter side of the same face, and height is the depth from the top opening down to the base. 18 × 12 × 10 inches and 12 × 18 × 10 inches describe two different boxes, so the order matters.
Can I work in millimetres instead of inches?
Yes. Inches are standard in Pakistan and that is what most enquiries arrive in, but millimetres are perfectly acceptable — just label which you are using. A number without a unit is the easiest way to get the wrong box.
Will the carton be exactly the size the calculator gives?
It will be made to a manufacturing tolerance, as all corrugated cartons are — board is scored and folded rather than machined, so a small variation across a batch is normal. Ask any supplier what their tolerance is before you order, particularly if the carton has to fit inside another one or onto a fixed shelf.
What if my product is an awkward shape?
Use the smallest rectangle the product fits inside — measure it at its widest, longest and tallest points, including anything that sticks out. If the shape wastes a lot of space, a die-cut box or a partition is usually the better answer than a bigger plain carton, and it is worth telling us what the product is.
