How to determine box size: an internal and external size guide
Box size is taken from the filled product and given as the internal size: the cavity reserved for the product. External size adds board thickness on top, and thickness varies by box type. Below you will find the measuring order, the length-width-height convention, clearance, inserts and the difference between internal and external size. The manufacturer converts exact values from the dieline.
Short answer: measure the product, give the internal size
To size a box, measure the product in its packed state at its widest point, add comfortable fit clearance and any insert thickness, and write the result as internal size (length × width × height, in millimetres). State the external size separately only when the box must fit a shelf, a carton or a shipping limit.
Key takeaways
Summary of this guide
- Take the measurement from the filled, packed product.
- Give the manufacturer internal size; write external size separately only for a shelf, carton or shipping limit.
- Write length, width and height in the same order, relative to the opening face.
- Take clearance and board thickness figures from the manufacturer; this page gives no universal numbers.
- Do not go to production before a prototype or white sample confirms the fit.
Internal size and external size
| Internal size | External size | |
|---|---|---|
| What it describes | The usable cavity where the product sits | The box’s outside dimensions |
| Board thickness | Not included | Included |
| Used for | Manufacturer quote, dieline, product fit | Shelf, carton, pallet and shipping limits |
| Who works it out | You (from the product) | The manufacturer (from dieline and material) |
- What it describes
- Internal sizeThe usable cavity where the product sits
- External sizeThe box’s outside dimensions
- Board thickness
- Internal sizeNot included
- External sizeIncluded
- Used for
- Internal sizeManufacturer quote, dieline, product fit
- External sizeShelf, carton, pallet and shipping limits
- Who works it out
- Internal sizeYou (from the product)
- External sizeThe manufacturer (from dieline and material)
Related glossary terms: Dieline, Board weight (GSM), Crease / score, Glue flap.
Measure the product in its packed state
Measure the product in the final state it enters the box. Parts that stick out, such as a cap, pump, dropper, shrink band or label, count. If several items go in, place them side by side as they will sit in the box and measure the group as a whole.
- Find the widest and longest points; for cylindrical products such as bottles, check diameter, shoulder and cap protrusion separately.
- For soft or shape-changing products (pouches, tubes), measure them filled.
- If possible measure several samples; production variation can shift the same product’s size slightly.
Write length, width and height in the right order
Box dimensions follow a fixed pattern: length, width, height. Which edge is which is set by the box’s opening face; the same three numbers in a different order can describe a completely different box structure.
- Length: the long edge of the opening face.
- Width: the short edge of the opening face.
- Height: the depth perpendicular to the opening face.
Some manufacturers or countries order them differently (for example width, length, height). To avoid confusion, say in words which order you use and which face opens, and give all values in millimetres.
Tip
Vertical or horizontal opening
The same dimensions give a different panel layout on a tuck-end box depending on which face carries the flap. To learn the panel names, see Reading a tuck-end dieline.
Add the fit clearance
A clearance is added so the product slides in and out comfortably. Its size depends on the product: a rigid, heavy product sits snugger, while a delicate or glass product may need more room and an insert for protection. A box that is too loose lets the product rattle; one that is too tight is hard to load.
There is no single clearance figure; take the value your manufacturer recommends and test it on a white sample. Product weight and fragility matter, and so does how the product goes into the box (by hand or on a line).
Account for inserts
Inserts such as card trays, EVA, foam or dividers take space from the internal volume. If an insert is used, add its thickness to the product size and write the internal size from that total. Inserts are not drawn in Grapxo; the printer or box maker cuts them.
In a box with an insert, the cut-out that holds the product and the box’s internal size are different things. Write both in the brief: the product size and the total internal size with the insert.
When do you give the external size?
External size matters when the box must fit a shelf, a shipping carton, an e-commerce shipping limit or a pallet. External size is internal size plus board thickness, and thickness differs markedly between folding carton, corrugated board and rigid box. The lid and fold structure also change how much is added outside.
So do not convert from internal to external by adding a fixed value. The exact external size comes from the manufacturer’s dieline. For shipping decisions see Shipper vs unboxing box and E-commerce box design.
Watch out
Say whether it is internal or external
If you send a single size line, write “internal” or “external” beside it. An unlabelled size is one of the most common misunderstandings in production.
Verify with the dieline and a sample
Once the internal size is set, the manufacturer or the dieline source produces the box’s flat layout. Compare the dimensions on the dieline with your brief. Then put the product into a paper model or white sample and test loading, removal and closing; only after that go to print.
Size checklist
- Was the product measured with cap, pump or dropper included?
- Are the values written length × width × height, in millimetres?
- Does the brief state clearly whether the size is internal or external?
- Was the insert thickness added to the internal size?
- Did the clearance value come from the manufacturer?
- Was the fit tested with a paper model or white sample?
For an example cosmetic brief see the Serum box size brief. For a general writing template see the Packaging brief template. To ask for a sample see the Sample box brief.
How do these steps run in Grapxo?
In Grapxo you write the product size and box type into the brief. The vector engine produces a dieline and an editable, layered vector surface from the brief; if a size changes, you revise on the same brief.
- The 3D preview in the browser is a visual check of the box; it does not replace testing whether the product physically fits.
- You take values such as clearance and inserts from the manufacturer; Grapxo assumes a 300 g/m² (0.389 mm) board when calculating creases.
- Final size approval and the print proof sit with you and the printer.
Start your box in the studio with the link below; for a category overview see Box design.
Frequently asked questions
Is box size given as internal or external?
Manufacturers are usually given the internal size, because it defines the cavity for the product. External size is written separately only for a shelf, carton or shipping limit.
How is the length, width, height order decided?
Length is the long edge of the opening face, width the short edge, height is perpendicular to it. If the manufacturer uses another order, say in words which face opens.
How do you go from internal to external size?
Board thickness is added to the internal size; but thickness and lid structure vary by box type, so adding a fixed value misleads. The manufacturer’s dieline gives the exact external size.
How much clearance should the product get?
There is no single figure. Take the value your manufacturer recommends, based on product weight, fragility and how it is loaded, and test it on a white sample.
Does Grapxo decide the box size itself?
No. You give the product size and the engine produces the dieline and vector surface from it; if you give no size, it suggests a sample size from the volume (marked as an example).
Start producing in the studio
Write your brief and let Grapxo produce a print-ready vector surface.