A box is measured Length by Width by Depth, always by the opening, with the longest side first. Length is the longer side of the opening, width is the shorter side, and depth, which some people call height, is the distance from the opening down to the base. Get those three numbers in that order and any packaging supplier can make your box or match one you already have. Here is how to measure a box correctly, how to size one around your product, and the one mistake that trips most people up.
The three numbers: Length, Width, and Depth
Look at the box from the open end. The length is the longer of the two sides of that opening. The width is the shorter side. The depth, which some people call height, is how deep the box goes from the opening down to the bottom. Always list them in that order, Length by Width by Depth, because a 10 x 8 x 4 box and a 4 x 8 x 10 box are two different things. Measure in inches to the nearest 1/8 inch for custom work.
Inside versus outside dimensions, the mistake to avoid
This is the one that causes reprints. Custom boxes are specified by their inside dimensions, because the inside is what has to fit your product. The outside is always a little larger because the board has thickness, so corrugated adds roughly 1/16 to 1/4 inch per wall depending on the flute, while cardstock folding cartons add very little. So when you give us a size, give us the inside measurement, or just send your product’s dimensions and we will build the box around it. Use outside dimensions only when you are checking shipping cost, pallet fit, or whether a box drops into a mailer slot.
How to size a box around your product
If you are starting from the product rather than an existing box, measure the product at its widest points for length, width, and height, then add clearance. For a snug retail fit, add about 1/8 to 1/4 inch to each dimension so the product slides in without forcing. If you are using an insert, foam, or padding, add room for that. For fragile items shipping on their own, leave space for cushioning on every side. Those inside numbers become your box’s inside dimensions.
Sizing for shipping cost
Carriers do not price by weight alone. They use a mix of weight and size called dimensional weight, so an oversized box can cost more to ship even when it is light. The fix is simple: do not buy more box than your product needs. A box sized close to the product means less void fill, a tidier unboxing, and a smaller dimensional footprint. This is exactly where a custom size beats jamming your product into the nearest stock box.
Custom size versus stock size
Stock boxes are fine when your product happens to match one. When it does not, you end up shipping empty space and padding it out. A custom mailer, product box, or shipping box cut to your exact dimensions solves that, and because we carry no minimum order, a custom size is realistic even for a first small run. For what a run costs at your size and quantity, see how much custom boxes cost, then request a quote with your dimensions and we will price it exactly.
Box measuring FAQs
How do you measure a box?
Measure the box by its opening, in the order Length by Width by Depth. Length is the longer side of the opening, width is the shorter side, and depth, or height, is the distance from the opening straight down to the base. Write those three numbers in that order and any supplier can make or match your box.
Are boxes measured by inside or outside dimensions?
Custom boxes are specified by inside dimensions, because that is what determines whether your product fits. Outside dimensions matter for shipping and storage, since the board adds thickness. If you are speccing a custom box, give the inside size. If you are checking whether a box fits on a pallet or in a mailer slot, use the outside size.
What order do box dimensions go in?
Length by Width by Depth, sometimes called height. Length is the longest side of the opening, width the shorter side of the opening, and depth the vertical measurement. Keeping this order avoids mix-ups, since a 10 x 8 x 4 box is very different from a 4 x 8 x 10.
How much clearance should I add around my product?
For a snug retail fit, add about 1/8 to 1/4 inch to each of your product’s dimensions so it slides in without forcing. If you are adding padding, foam, or an insert, add space for that too. For fragile items in shipping boxes, leave room for cushioning on all sides.
Does box thickness change the size?
Yes, a little. Corrugated board adds roughly 1/16 to 1/4 inch per wall depending on the flute, so the outside of a corrugated box is bigger than the inside. Cardstock folding boxes add very little. We work from your inside dimensions so the product fit is always right.
Should I use a custom size or a stock box?
If your product does not fit a stock size well, a custom-cut box usually wins, since you get less void fill, a cleaner unboxing, and often a lower shipping cost because you are not paying to ship empty space. Since we have no minimum order, a custom size is realistic even for a small run.
Related ordering guides
Getting an order ready? See how to set up print-ready box artwork and how long custom boxes take to make.
