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Inside, outside and crease-to-crease dimensions: the difference

Three dimensions describe the same carton and still produce different numbers. The difference comes from material thickness and from folding.

Inside dimension: what fits inside

The inside dimension describes the usable space in the assembled packaging. It is the appropriate starting point if a product is to fit inside. For corrugated board, inside dimensions are the usual reference, and the FEFCO code also gives dimensions as inside dimensions. The inside dimension includes the clearance for inserting and removing the product. Flaps folded inward can further reduce the usable space. Only a sample with the real product shows whether the space is sufficient.

Outside dimension: what needs space

The outside dimension describes the external dimensions of the assembled packaging. You need it when the carton has to fit into a shipping carton, a shelf or a display. Because of material thickness, it is larger than the inside dimension. How much larger depends on more than just the thickness. Overlapping surfaces, for example at the glue flap or the bottom, add up in places. Therefore check the outside dimension on the assembled sample and not only on the flat drawing.

Crease-to-crease dimension: what is on the drawing

The crease-to-crease dimension is the distance between the crease lines of a panel on the flat blank. Cutting dies and cutting tables work with this dimension. The crease-to-crease dimension is neither the usable inside space nor the external dimension. The conversion depends on material, creasing and construction. If a printer gives you dimensions from its drawing, ask which reference they use. Two drawings with the same numbers can describe cartons of different sizes if the reference is not the same.

Why the dimensions differ

When folding, the material wraps around the crease and uses up length in the process. The thicker the material, the greater this effect. Crease compensation distributes the material thickness across the panels. Outer panels tend to receive more allowance than inner panels. Flaps that fold inward are shortened so they do not hit each other. For corrugated board, the allowances are larger and depend on the flute direction. There are no fixed conversion values. Reliable values come from measuring a test piece made from your material.

Record the dimension reference clearly

Write the reference and the unit with every dimension, in the inquiry as well as in the approval. Ask when someone gives you dimensions without a reference. In JetDieline you choose whether your input refers to inside dimension, outside dimension or crease-to-crease dimension. The allowances and reductions are set out in the chosen material profile. Bundled profiles are starting values and not a measurement of your carton. If you import a contour from your printer, clarify unit and dimension reference before comparing.

Step by step

  1. Clarify the purpose: should the product fit inside, or should the carton fit into something else?
  2. Then choose inside dimension or outside dimension as the reference.
  3. Write the dimension reference and the unit with every number.
  4. Agree on the material and material thickness with your printer.
  5. Check the dimensions against the assembled sample.

Frequently asked questions

Can I calculate the outside dimension from the inside dimension and material thickness?

Only approximately. Overlapping surfaces and the crease affect the result. You measure the actual outside dimension on an assembled sample made from the intended material.

Which dimension appears on my printer's drawing?

That varies by print shop and packaging type. A die drawing often shows crease-to-crease dimensions, and inside dimensions are usual for corrugated board. Ask explicitly before you compare numbers.

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