L × W × H: How to Measure Box and Bag Dimensions Correctly

Knowing how to measure box dimensions correctly is the most basic skill in custom packaging, and the one that causes the most rework. A dimension written in the wrong order, an outer size mistaken for an inner one, or a centimetre read as an inch is enough to make 5,000 boxes that your product does not fit. This guide explains exactly how to measure a box, a mailer and a bag the way factories quote them: what length, width and height refer to, why inner, outer and flat measurements are three different numbers, how to turn L × W × H into CBM for freight, and how to check your product against the real stock size grids in our catalogue before you commit to an order.

L × W × H: which dimension is which?

L × W × H stands for length × width × height, always given in that order. Length is the longest dimension of the opening face, width is the shorter side of the same face, and height (also called depth) is how far the box rises from that face. A 24.5 × 14 × 8.5 cm drawer box therefore has a 24.5 cm opening edge, a 14 cm side edge and an 8.5 cm tall tray.

The convention holds even when the numbers feel interchangeable: on a nearly square box the factory still expects longest first, and rotating the product 90 degrees does not change which edge is length — the box geometry does. Measure with the opening facing you and the box sitting flat on a table, never holding it in the air, because a tilted box measures a few millimetres larger across its diagonal every time. Use a rigid tape or a steel rule; a soft tailor's tape curved across the opening overstates the reading.

How to measure box dimensions in five steps

Whether you are measuring an existing sample you want to replicate, or the product you need a box for, the procedure is the same. Measure in millimetres if you can — 220 × 90 × 45 mm leaves no room for the rounding errors that hide in 'about 22 by 9 by 4' — and record every number as L × W × H.

1. Set the box on a flat surface with its opening facing up. If it is a two-piece lid-and-base box, measure base and lid separately.
2. Measure the inside of the opening: edge to edge along the longest inside face (length), then the shorter inside face (width). Push the tape flush into the corners — a tape stopped on the rim reads 1–2 mm short.
3. Measure inside height from the bottom panel to the top edge. For a drawer tray, measure the tray, not the sleeve.
4. Measure the outside the same way if you need to plan master cartons or pallet loading: longest outer edge, shorter outer edge, floor-to-lip outer height.
5. Write both sets with labels: inner 160 × 100 × 55 mm, outer roughly 166 × 106 × 62 mm. Never send a supplier three bare numbers without saying inner or outer.

Inner vs outer vs flat dimensions: three different numbers

Most sizing disputes come from treating these as one number. Rigid gift boxes are quoted by inner dimensions, because the inner tray is engineered around your product; the wrapped outer sleeve adds 4–8 mm of board on every axis. Corrugated mailers are usually quoted by outer footprint, because that is what courier rate cards and mailer bags are priced on. Asking 'how big is the box?' gets you whichever number the seller happens to use, so always ask which one is listed.

Flat dimensions matter for freight and storage. A magnetic folding box that is 24 × 18.6 × 10.6 cm erected travels as a flat blank around 30 × 22 × 2 cm; a pallet of them ships at a fraction of the erected volume. The same applies to corrugated mailers, which nest flat before fulfilment. If you are comparing two suppliers on shipping cost, compare flat-packed volumes per master carton, not the erected size on the product page.

How to measure bags: gussets and the drawstring allowance

Soft packaging does not have rigid inside edges, so it is measured flat, and the third dimension behaves differently. A paper carrier bag is listed as width × height × gusset — for example our white-card bags run from 12 × 16 × 5.7 up to 22 × 18 × 10 cm — where the gusset is the folded pleat across the side and bottom that opens into the bag's depth. A 10 cm gusset on a 22 cm-wide bag opens into a roughly rectangular footprint; a bag with no gusset stays a flat envelope no matter how wide it is.

Drawstring pouches are quoted as flat width × height, but you cannot use the full height. The cord channel across the top consumes roughly 2 cm: a pouch marked 15 × 20 cm gives about 15 × 18 cm of usable fill length, and the cinched opening also narrows by a centimetre or so on each side. When a rigid item — a gift-card box, a phone, a small book — is going into a pouch, size against the pouch's usable rectangle, not its printed flat size, and step up one tier if the item is borderline. That single rule prevents most 'it should have fit' reorders.

Turning L × W × H into CBM for shipping

Once boxes are packed into master cartons, the same three measurements drive freight. One carton's volume in cubic metres is L × W × H in metres; if you measure in centimetres, multiply L × W × H and divide by 1,000,000. A 60 × 40 × 40 cm master carton is 0.096 CBM, and 500 of them are 48 CBM — already more than a 20 ft container's usable space, a fact much cheaper to discover on paper than at the dock.

Air freight converts the same volume into volumetric weight using the industry divisor 6,000: L × W × H in cm ÷ 6,000 = volumetric kilograms. The airline bills the greater of that figure and actual gross weight, which is why light, bulky cartons cost more to fly than their scale weight suggests. Choosing flat-packed and nested formats lowers both numbers without changing the product inside.

Real stock sizes: check your product before tooling anything

These are the actual size grids currently in production. If your product fits a stock inner size with standard clearance, the structure and cutting die already exist: MOQ starts at 50–100 pieces and logo orders dispatch in about 7–10 days. Only a size outside the grids needs a new dieline and a custom run, which typically starts around MOQ 500.

Clearance rules: how much room to add

Packing a box to the millimetre is not a goal. Paper and board need clearance to assemble, and your product needs room for an insert and fingers to lift it out. The working rules below are what production samples are checked against; the white sample is where exact fit is finally signed off.

• Rigid boxes: aim for about 5 mm clearance on each horizontal axis once the insert is in. Zero clearance jams the tray; over 10 mm lets the product rattle and feel cheap.
• Mailers: the listed size is the outer footprint, so subtract flute and crease allowance before assuming fit. A product near the listed inner limit should be checked on a sample, not ordered direct.
• Inserts and padding: add their thickness to the product before sizing the box. A 5 mm foam bed adds 5 mm to height, and a wrapped or dust-bagged product adds 2–4 mm on the width.
• Pouches: use the flat size minus the ~2 cm cord channel, and choose the next tier up for rigid items near the limit.
• Bottle and candle orders: always measure across the cap or lid, which is wider than the body more often than buyers expect.

Five measuring mistakes that ruin packaging orders

1. Swapping inner and outer. Ordering a box from an outer-size listing as if it were inner space is the classic mismatch; rigid boxes quote inner, mailers quote outer.
2. Mixing centimetres and inches. A '9 × 6 × 4' written without a unit has been read wrong on every continent. Put cm or in after every set.
3. Reordering the numbers. Width first, length second turns a long drawer into a square tray. Always longest first: L × W × H.
4. Measuring the product at its slimmest. Caps, seams, folded hems and gift wrap add bulk. Measure the bulkiest configuration you will actually ship.
5. Ignoring the flat-packed volume. A beautifully sized erected box that throws away half the container costs you margin on every reorder. Ask for the flat carton dimensions too.

How to send dimensions in an RFQ

The clearest enquiries our sales team receives all use the same one-line format, and they are quoted fastest because nothing has to be guessed: product is X × Y × Z mm at its bulkiest, insert adds N mm, required inner size is A × B × C mm, quantity Q, format preference (drawer / mailer / pouch). Add whether the figures are mm, cm or inches, whether a stock size may be substituted, and your destination country so freight can be estimated on flat-packed volume.

Box and bag dimension FAQ