How to measure your box size
Length, width and height, inside dimensions, inserts and the mistakes that make boxes not fit. This guide covers length, width, height: in that order, inside or outside dimensions? and how to measure your product. It is written by our packaging team, drawing on 15+ years of designing and printing boxes.
8 October 2026 · 4 min read
Last updated
Written by the packaging team at The World of Packaging.
The most common reason a box does not fit is a measuring mix-up, not a production error. Here is how to measure so your quote and your box are right first time.
Length, width, height: in that order
Box sizes are always written L × W × H:
- Length: the longer side of the opening.
- Width: the shorter side of the opening.
- Height: the depth, from the opening to the base.
The opening is the side that opens. For a tuck end box that stands upright, the opening is on top, so the "height" is the tall side. For a mailer, the opening is the lid, so the height is usually the shortest side.
Inside or outside dimensions?
We work from inside dimensions: the space your product needs. Board thickness is added on the outside. This matters most for rigid boxes, where 2 mm greyboard plus wrap adds several millimetres to each side.
If your box must fit into something else, such as a shipping carton or a shelf, tell us the maximum outside size as well.
How to measure your product
- Measure the product at its widest points, including caps, pumps and handles.
- Add space for anything else in the box: inserts, tissue, cards or accessories.
- Add a small allowance so the product slides in without forcing. A few millimetres is usually enough; an insert takes up the rest.
- Round to the nearest millimetre and note whether the figures are in mm or inches.
When there is an insert
An EVA, card or pulp insert needs its own thickness around the product. Send us the product size and we size the insert and the box together. For unusual shapes, a physical product or a technical drawing gives the best fit.
Common mistakes
- Measuring the outside of an old box and sending it as the inside size.
- Mixing up width and height on upright boxes.
- Forgetting the cap or pump on bottles.
- Leaving no room for a thank-you card or leaflet.
Check it before printing
Before production you approve a digital proof with the dieline and a 3D mockup, so the size is checked before anything is printed. If you are unsure, send us the product dimensions and we will suggest a size. You can also start a quote with approximate figures and refine them later.
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