A few factors need to be kept in mind: How much clearance is required around a product? It’s certainly not something you can quickly eyeball off of the dimensions listed for a product. The proper size of a mockup is derived from the actual dimensions of the product, as well as the parts that might extend out of the main body, are squishy, move, or reposition when being packed.
To start the mockup, put the product in a fixed position on a flat surface and decide how you’d want it placed in the package. Grab your metal ruler, a measuring tape, or even calipers if you’re feeling fancy, and determine the widest, tallest, and deepest points that can be made in this orientation. Don’t just take the product from its largest body part. Measure across any handles, caps, folds, cords, protruding buttons, or awkward surfaces. Jot down the measurement and add a quick note for which side of the product this is measuring. This will save you a lot of trouble from swapping width and depth later on when you’re putting together your dieline.
Never use your product dimensions as a template or reference for how your package will end up in its interior. Your package is designed with the product inside, after all. The reason a structure based purely on the product dimensions might not work out is that it could potentially end up being too small, even for the slightest of adjustments due to material thickness, fold resistance, seaming, and manufacturing tolerances. Having clear space allows the product to get into the package, without needing a lot of force to get in or out. The clear space depends on material and the product shape, whether it’s using a lid or other closures, and any additional insert or protection that might be used inside. The best way to ensure clear space is through a mockup, rather than just a specific number for tolerance.
There will be times when the product is soft or irregular in some way, like a bag of something, folded piece of fabric, coiled cable, or other flexible items. These things won’t maintain the same dimensions, regardless of which way it’s being measured. For these scenarios, measure it in the form you’d actually pack it in and try packing it a few times to notice if there is any variance in size or if it’s more expansive in either direction and pressing more against either side. For fragile items, include the thickness of tissue paper or foam inside, if used to protect the item. Don’t try to add protection outside, after the fact.
Material thickness changes things too. A mockup constructed from regular paper can help determine which way panels go and general dimensions, but will definitely be different than the actual paperboard or cardboard you will end up using, even more so depending on the material thickness. It could take up a lot of space from your fold and make your closure difficult to insert. Corrugated will also add some significant space to your package, inside and out. This is when you go back to your mockup from your previous material choice to your new material choice to ensure internal dimensions work well, the folds work well, you know where your seams are and how your package closes.
The very next thing you do after finishing your mockup is actually put the product in it. No squeezing! Just put it in, turn the box over, open and close your mockup several times, and then take the product out. Check for crushed corners, bulging panel walls, loose movements, weak seams or weak places on the closure flaps that could be the product getting caught in them. There could even be enough overall volume in a mockup but have poor fit due to the clear space not being where it’s needed to ensure proper clearance. Make notes directly on the mockup and update your specifications sheet before modifying your dieline.
Accurate measurements will determine a package that can securely hold a product without crushing it, or allow too much slack movement. Before finalizing your mockup and product dimensions, always check with these questions before you put it through production: can you repeatedly pack and unpack, protect, close, open, and remove the product as needed?