How do you measure for a custom box?
Measure the product at its widest points and give dimensions as Length × Width × Height in that order. Custom boxes are built to internal dimensions, so add a small allowance for easy fit — plus extra space if you're using an insert or protective wrap.
Length, width and height explained
- Length — the longer side of the box opening.
- Width — the shorter side of the box opening.
- Height (depth) — the distance from the opening to the base.
Always quote them in the same order. "20 × 15 × 8 cm" and "8 × 15 × 20 cm" are different boxes — one opens on the large face, the other on the small end.
Internal vs external dimensions
Board has thickness. A rigid box or a 5-ply corrugated box can be noticeably larger on the outside than the inside. Packaging is designed from internal dimensions (so the product fits), but shipping costs are calculated from external dimensions — so keep both in mind.
How much allowance should you add?
| Situation | Typical allowance |
|---|---|
| Snug retail carton | A few millimetres on each side for easy insertion |
| Product with a paperboard insert | Insert thickness on each side, plus fit allowance |
| Fragile item with cushioning | Enough space for the cushioning material on all sides |
| Multiple items in one box | Measure the items as arranged together, then add allowance |
Common measuring mistakes
- Measuring the product without its cap, pump or handle.
- Forgetting the thickness of inserts, tissue or bubble wrap.
- Mixing up millimetres, centimetres and inches.
- Not checking how the box opens — top-loading or end-loading.
Why right-sizing saves money
An oversized box needs more board, more filler and often costs more to ship, because many couriers charge by volumetric weight. A right-sized box looks better, protects better and reduces cost on every order.
Not sure about the size?
Send us the product or its measurements and we'll create the dieline and a prototype so you can check the fit before production. Packaging prototyping →
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