Packaging Fundamentals · Quick guide
How to Measure a Box Correctly (L × W × D)
Published Reviewed
Measure a box from the inside, in millimetres, and write the three figures in a fixed order: length × width × depth. Length and width are the two sides of the opening, with length the longer, and depth runs from the opening down to the base. For a new custom box, measure the product rather than an old box, add a small clearance, and send those internal figures to your supplier.
Why internal dimensions come first
The one thing a box must do is fit what goes in it, so custom packaging is specified by the space inside. Your supplier draws the dieline from the internal dimensions and adds the board thickness, the flaps and the folding allowances needed to reach that space once the box is made up.
External dimensions still matter. They decide which postal size band a parcel falls into, how many boxes fit in an outer carton and whether a pack fits the shelf. But they are the result of the internal size plus the board, not the starting point. Our guide to internal vs external dimensions covers when to use each.
Length, width and depth: why the order matters
The order of the three figures tells the supplier where the box opens. Length and width always describe the opening, with length the longer side; depth is the distance from the opening to the base. Reverse the order and you describe a different box.
A carton written as 60 × 40 × 150 mm is tall and narrow and opens at the top, like a fragrance or toothpaste carton. The same three numbers written as 150 × 60 × 40 mm describe a wide, shallow box that opens across its largest face. Same volume, completely different pack.
| Box type | Where it opens | Length × width | Depth |
|---|---|---|---|
| Straight tuck end carton | Through the end panel | The end (the tuck lid) | The height of the body |
| Roll-end tuck front mailer | Lid lifts across the top | The footprint | The shallow height |
| Lid and base box | Lid lifts off the top | The footprint of the base | The height of the base |
| Drawer box | Tray slides out of a sleeve | The footprint of the tray | The height of the tray |
Some suppliers write L × W × H. Height and depth mean the same thing here, and the rule about the opening still applies.
How to measure your product
Measure the product as it will actually go into the box, then work outwards.
- Measure at the widest points. Include caps, pumps, lids, handles, hanging loops and anything that sticks out. A bottle's shoulder is rarely its widest point once the cap is on.
- Measure the packed item. If the product sits in a pouch, a jar, tissue or a sleeve, measure that rather than the bare product.
- Use the right tool. Digital callipers or a steel rule read to the millimetre; a cloth tape measure does not.
- Measure several units. Handmade, poured and glass products vary. Size the box to the largest one you expect to pack.
- Weigh it. Weight decides the board and whether the box needs a stronger base, such as a crash-lock bottom.
- Decide which way up it goes. Choose which face the customer should see first, because that face sits under the opening.
How much clearance to allow
Clearance is the small gap between the product and the inside of the box. Too little and the product will not go in, or the panels bulge. Too much and it moves in transit, needs void fill and makes a bigger parcel than necessary.
The figures below are typical starting points. The right allowance depends on the board, the style and how the product is packed, and it is confirmed on the dieline before you approve the proof.
| Packing situation | Typical clearance on length and width | Typical clearance on depth | Why |
|---|---|---|---|
| Single rigid product in a folding carton | About 1–2 mm | About 1–3 mm | Slides in without rattling; tuck flaps still close flat |
| Product wrapped in tissue in a mailer | About 3–5 mm or more | About 3–5 mm or more | Tissue and a message card take up space |
| Product held in an insert | Sized to the insert | Sized to the insert | The insert grips the product; the box is sized around the insert |
| Rigid box with a lift-off lid | About 1–2 mm on the base | Set by the lid depth | The lid must slide over the base without catching |
| Several items in one box | About 2–3 mm across the group | About 2–3 mm | Allows for small variations between units |
If the product is held in a custom insert, give us the product size and let us size the insert and the box together. The insert changes the internal dimensions the box has to provide.
What board thickness adds
The board has thickness, so the outside of a box is always bigger than the inside. As a working rule, each dimension grows by about twice the board thickness, once for each wall. Some styles add more, because flaps or folded walls double the board in places.
| Board | Approximate thickness | Roughly added to each dimension |
|---|---|---|
| Folding boxboard, 300–400 gsm | About 0.4–0.6 mm | About 1 mm |
| E flute corrugated board | About 1.5 mm | About 3 mm |
| B flute corrugated | About 3 mm | About 6 mm |
| Double wall corrugated (EB or BC) | About 4–7 mm | About 8–14 mm |
| Greyboard for rigid boxes, with its wrap | About 1.5–3 mm plus the paper | About 3–6 mm, more where a lid sits over the base |
Thicknesses vary by mill and grade, so treat these as guides. The exact figure for your board is built into the dieline. Our guide to GSM and board thickness explains how weight and calliper relate.
Measuring a box for several products
If one box holds a set of items, such as candles, jars or cartons packed together for postage, work out the arrangement first and then add up the dimensions. This is the calculation the old box-packing calculator did, and it is simple to do by hand.
- Decide the grid: how many items along the length, how many across the width and how many layers.
- Multiply the product size by the number of items in each direction.
- Add the thickness of any dividers or layer pads between the items.
- Add clearance across the whole group.
Worked example. Twelve jars, each 70 mm in diameter and 85 mm tall, packed upright in a four by three grid with E flute dividers about 1.5 mm thick.
| Direction | Calculation | Internal dimension |
|---|---|---|
| Length | 4 jars × 70 mm, plus 3 dividers × 1.5 mm, plus 2 mm clearance | About 287 mm |
| Width | 3 jars × 70 mm, plus 2 dividers × 1.5 mm, plus 2 mm clearance | About 215 mm |
| Depth | 85 mm jar height, plus 3 mm clearance | About 88 mm |
The internal size is about 287 × 215 × 88 mm. In B flute, the external size would be roughly 293 × 221 × 94 mm. Try more than one grid: a three by four layout, or two layers of six, can give a smaller, squarer box or a lighter parcel. Right-sizing the grid is one of the easiest ways to cut void fill and carriage.
Common mistakes
- Measuring an old box from the outside. You end up with a new box that is a board thickness too big on every side. Measure the product, or the inside of the old box.
- Writing the figures in the wrong order. The opening moves, and the product goes in sideways.
- Forgetting what sticks out. Pumps, caps, hanging tabs and handles are the usual culprits when a product will not close in its box.
- Allowing clearance twice. If you add clearance and do not tell your supplier, they add it again and the product rattles.
- Sizing to one sample of a variable product. Hand-poured or blown-glass items can differ by a few millimetres. Measure several.
- Ignoring the insert or wrap. Tissue, a card or a cradle all take space and must be in the numbers.
What to send with your quotation request
Send the product's length, width and depth in millimetres, its weight, and how it is wrapped or held. Add the box style you have in mind, the quantity and any outside size limit, such as a postal band or a shelf. If you already have internal box dimensions, label them as internal.
That is enough for us to draw a dieline and show you the size before anything is made. Our guide to the information needed for a quote lists everything else that helps, and you can send it all through the quote form.