Packaging guide
How to measure a carton
The single most common specification mistake, and how to avoid it — internal dimensions, in the right order, with the right clearance.
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In short
- Always give internal dimensions — the space inside the carton, measured to the inside faces.
- Write them length × width × height. Length is the longer side of the open face, width the shorter, height the depth.
- Inches are standard here. Millimetres are fine too — just label which you used.
- External dimensions include the board, so the same external size gives you less room in 5-ply than in 3-ply.
- Allow a few millimetres of clearance around the product, and more if it has an insert or a surface that must not scuff.
Internal, not external
This is the mistake that costs money, and it is worth stating before anything else. Give the dimensions of the space inside the carton — measured to the inside faces of the four walls, and from the inside of the base to the top opening.
External dimensions are the size of the finished box including the board. That sounds like a small difference and it is not, because board thickness changes with ply. A carton ordered at “18 inches” externally gives you noticeably less room in 5-ply than in 3-ply, and less again in 7-ply. Order externally and change the board later, and the product that used to fit no longer does.
| Board | Approximate wall thickness | Roughly lost across a dimension |
|---|---|---|
| 3-ply | ~3 mm | ~6 mm (two walls) |
| 5-ply | ~7 mm | ~14 mm (two walls) |
| 7-ply | ~12 mm | ~24 mm (two walls) |
These are indicative figures — actual thickness depends on the flute profile and the paper. The point is the size of the effect: on a 7-ply carton the difference between internal and external is close to an inch across the box.
Length, width, height — in that order
The convention across the trade is length × width × height, and it is not arbitrary:
- Length is the longer of the two sides of the open face.
- Width is the shorter side of that same face.
- Height is the depth — from the top opening straight down to the inside of the base.
Look down into the open box: the two numbers you see are length and width, longer first. The one you cannot see from above is the height.
Order matters. 18 × 12 × 10 and 12 × 18 × 10 describe two different cartons, and only one of them holds your product the way you intended.
Inches, and say so
Inches are the working unit in Pakistan — every enquiry we receive is in inches, and so is every listing you will find locally. Millimetres are perfectly acceptable if that is what your drawings use.
The one rule is to label the unit. “18 × 12 × 10” with no unit is ambiguous, and the two readings are wildly different boxes.
Measuring a box you already have
The reliable method is to open the carton, stand it upright, and measure inside the walls with a tape held against the inside face. Take the height from the inside of the base to the top edge, ignoring the flaps.
If you can only measure the outside, subtract about twice the wall thickness from the length and the width, and roughly the same from the height, using the table above. Treat the result as an estimate.
Better still, send us the box. A sample removes every source of error at once, and we can measure the board grade off it as well as the dimensions.
Measuring from the product instead
If there is no existing carton, measure the product and add clearance. Work in the same order — the longest dimension of the product becomes the length, and so on.
Add allowance for:
- Clearance — a few millimetres on each dimension, so the product goes in without forcing and does not rattle in transit.
- Inner packaging — bubble wrap, a bag, a foam pad, a printed sleeve. Measure the product as it will actually be packed, not bare.
- Partitions or inserts — if bottles or jars are separated by dividers, the dividers occupy real space. See partitions and inserts.
- How many per carton — if six units go in two rows of three, the carton is sized to the arrangement, not to one unit.
A worked example
Say you are packing twelve bottles, each 3 inches across and 9 inches tall, in three rows of four, with dividers between them.
| Step | Working | Result |
|---|---|---|
| Bottles along the length | 4 × 3 in | 12 in |
| Bottles across the width | 3 × 3 in | 9 in |
| Height | Bottle height | 9 in |
| Add dividers and clearance | Roughly ¼ in on length and width | 12¼ × 9¼ × 9¼ in |
| What you send us | Internal, L × W × H, in inches | 12.25 × 9.25 × 9.25 |
Tolerance: cartons are folded, not machined
A corrugated carton is scored and folded from board, so a finished box carries a small manufacturing tolerance — a few millimetres of variation across a batch is normal and expected everywhere in the industry.
That matters when the carton has to fit inside something else: a master carton, a fixed shelf, a pallet footprint, or a container. If your job is that tight, say so with the enquiry and ask your supplier what tolerance they work to before you place the order.
The five mistakes we see most
- Sending external dimensions without saying so.
- Giving the numbers in the wrong order, so length and width swap.
- Leaving the unit off entirely.
- Measuring the product bare, then adding inner packaging afterwards.
- Measuring a flattened carton across the fold, which reads short.
Where to go next
- 3-ply, 5-ply or 7-ply — the ply that decides your wall thickness.
- What is a master carton? — sizing an outer around inner boxes.
- Glass and crockery boxes — measuring a tapered glass or a mug with a handle for its partition cell.
- GSM and BF explained — the paper grade half of a specification.
Common questions
Should I give internal or external dimensions?
Always internal, unless you say otherwise. Internal dimensions are the space your product has to fit into, measured to the inside faces of the carton. External dimensions include the thickness of the board, which changes with ply — so an external measurement means a different internal space depending on the board used, and your product may not fit.
In what order should I write the dimensions?
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. Writing 18 × 12 × 10 inches and 12 × 18 × 10 inches describes two different boxes, so the order matters.
Inches or millimetres?
Inches are standard in Pakistan and that is what most enquiries arrive in. Millimetres are perfectly acceptable too — just label which you are using, because a number without a unit is the easiest way to get the wrong box.
How do I measure a box I already have?
Open it, stand it up, and measure inside the four walls to the inside faces — not across the outside. If you can only measure the outside, subtract roughly twice the board thickness from the length and the width, and about the same from the height. That is an approximation, so send a sample where you can.
How much clearance should I allow around the product?
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.
Will the finished carton be exactly the size I asked for?
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 and expected. 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.
