Internal or external dimensions? This is how you read box dimensions and measure them yourself
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by Verpakkingdeals.nl
6 min reading time
Box dimensions are sometimes listed as inner and sometimes as outer measurements. Here's how to measure your product, how much allowance you should give, and why height is the most important dimension.
You order one hundred boxes of 15 x 10 x 4 cm, and when they arrive, your 15 cm product just doesn't fit. Or worse: it fits, but there's no room left for a sheet of paper, let alone a piece of bubble wrap. Almost always, this is due to the same misunderstanding: the size in the webshop is not the size you had in mind.
Internal dimensions, external dimensions and why they differ
A cardboard box has two sets of dimensions. The internal dimensions are the space your product fits into. The external dimensions are what the carrier measures and what appears on your pallet or in your cupboard. The difference is the thickness of the cardboard plus the fold, and for single-wall cardboard, this quickly amounts to several millimeters per side.
For shipping boxes and letterbox boxes, the dimensions are usually given as internal dimensions, because you want to know what fits inside. For gift boxes and presentation boxes, the external dimensions are more often stated, because appearance matters. If it's not specified? Assume the least favorable case and allow a few extra millimeters. If you are in doubt about a large order, please check via info@verpakkingdeals.nl before bringing in a thousand units.
How to measure your product
Always measure the product as it will go into the box, including its own packaging, sleeve or label. Work in millimeters to avoid rounding errors.
Length: the longest side, flat on the table.
Width: the second side, perpendicular to the first.
Height: the thickest point. Pay attention to protruding parts such as a cap, knob, zipper or a book spine.
If you have several variants of the same product, measure the largest one. One box size for your entire assortment is cheaper and faster to pack than five sizes that you have to distinguish by feel.
How much clearance should you allow?
Clearance is not waste, it's protection. Rules of thumb that work well in practice:
Type of shipment
Clearance per side
Why
Clothing, textiles, soft
5 to 10 mm
Fills itself, low risk
Small boxes, books, boxes in boxes
10 to 15 mm
Space for tape and a void fill sheet
Fragile (glass, ceramics)
30 to 50 mm
Space for padding all around
Too much clearance is also a problem: a half-empty box will shift and collapse if something is placed on top of it. If you can move the product back and forth in the box with your hand, the box is too large or needs more filling.
Height is the critical dimension
For letterbox mail, height is the dimension that determines whether your package fits through the letterbox or is handled as a parcel, and that saves money. PostNL allows a maximum of 38 x 26.5 x 3.2 cm and a maximum of 2 kg for a letterbox package; always check the PostNL customer service page for the current conditions, as rates and dimensions may change.
So first measure your product at its thickest point. If you are at 30 mm, letterbox mail is no longer an option and you should immediately opt for a parcel box, for example the Cardboard Shipping Box 15 x 15 x 15 cm for € 1.99.
Calculate to price per shipment
Choosing box sizes also involves calculation. A bundle of 100 A6 letterbox boxes for € 17.95 comes down to approximately € 0.18 per box; for the A5+ bundle of 100 for € 24.00, you are around € 0.24 each. Loose boxes are more expensive per piece, but you'll lose less if a size doesn't work out.
Measure your product in millimeters at its thickest point, check if the specified size is an internal or external dimension, add the clearance appropriate for your product, and only then check the price per piece. In that order, you'll rarely buy the wrong box.
If you want to compare: all formats are available at Packaging & Shipping, the flat variants at Letterbox Packaging, and the presentation variants at Gift Packaging & Gift Boxes and Boxes. If you can't figure it out with measuring or are in doubt between two sizes for a larger order? Email the dimensions of your product to info@verpakkingdeals.nl, and we'll help you think it through.
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