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27 Oct 2026 · 5 min read · Measuring & dielines

How to Measure a Custom Box: Inside Dimensions, Dielines and Samples

The most common sizing mistake is simple: measuring the outside of an existing box and ordering that size. Board thickness, folds and inserts all eat into the space your product actually gets. Measure from the inside, in this order, and most problems disappear.

Step 1: Measure the product, not the old box

Measure the product at its widest, deepest and tallest points, including any cap, lid or protruding part. Then add the insert: if you need foam, pulp or a corrugated divider, its thickness counts too. A box that fits the product exactly, with no room for an insert, is already too small.

Step 2: Give it breathing room — on purpose

Allow a small, deliberate clearance so the product slides in without forcing the closure, but not so much that it rattles in transit. For most rigid and mailer boxes, a few millimetres of clearance per side is a good starting point; your factory can confirm the exact allowance once it knows the board and structure.

Step 3: Record inside dimensions, in order

Always write length × width × height, and say whether those are inside dimensions. Our configurator uses inside dimensions in inches, so a spec like “8 × 6 × 4 in, inside” leaves no ambiguity. If you work in centimetres, send those too — the conversion is trivial, the guesswork is not.

Step 4: Get a dieline before you approve artwork

A dieline is the flat, production-ready outline of your box: every fold, glue flap and cut line, at real size. Our structural designers build a dieline free within 24 hours from your product dimensions. Artwork should be placed on that dieline, not on a guess, and print files should be print-ready PDF or AI at 300 dpi in CMYK.

Step 5: Sample before mass production

Blank structural samples are free; printed colour proofs take 3–5 working days, and you only cover the courier. A sample answers questions no rendering can: does the lid close cleanly, does the insert hold, does the colour match your Pantone reference? It is the cheapest insurance in the whole order.

Common mistakes to avoid

• Measuring outside dimensions and forgetting board thickness.
• Forgetting the insert, tissue or protective wrap in the height.
• Ordering a magnetic rigid box without checking the lid clearance.
• Approving artwork before the dieline is confirmed.