The right mailer box size is the smallest one your product fits in with enough room for protection, that also stays under your carrier's next price band. Too big and you pay to ship air and need more filler. Too small and the product arrives damaged or the lid bulges.
Here is how to find the right size, with the standard sizes many suppliers stock and a worked example from tape measure to spec.
Standard sizes
| Name | Internal mm (L x W x H) | Internal in | Good for |
|---|---|---|---|
| Small | 152 x 102 x 51 | 6 x 4 x 2 | Cosmetics, jewellery, small accessories |
| Medium | 203 x 152 x 76 | 8 x 6 x 3 | Subscription boxes, a folded T-shirt |
| Medium wide | 229 x 152 x 76 | 9 x 6 x 3 | Books, stationery |
| Large | 254 x 203 x 102 | 10 x 8 x 4 | Multi-item kits, two or three products |
| Large flat | 305 x 229 x 102 | 12 x 9 x 4 | Apparel, prints |
| Extra large | 305 x 254 x 152 | 12 x 10 x 6 | Gift sets, footwear |
These are typical sizes, and your supplier may stock slightly different ones. Custom sizes are also possible; ask your supplier how minimums and pricing compare with their stock sizes.
How to measure your product
Measure the product (or the stack of products) at its widest points: length, width, height. Measure with any retail packaging it already has, and include anything else that goes in the box, such as a card or a sample.
Then add room for protection. As a rough guide, allow 6 mm to 10 mm on each side for tissue or paper, and 20 mm or more each side if you need foam or moulded inserts. Round up to the nearest standard size, or specify custom internal dimensions if the standard sizes leave a lot of empty space.
Worked example
Say you sell a candle in a gift tin, plus a folded care card.
- Measure. The tin is 95 mm across and 70 mm tall. The card lies flat on top and adds almost nothing.
- Add protection. You plan to wrap it in tissue, so you add 8 mm each side: 95 + 16 = 111 mm across, and 70 + 16 = 86 mm tall.
- Compare with stock sizes. The small box is only 51 mm tall, too shallow. The medium (203 x 152 x 76) is too shallow as well and much longer than you need.
- Decide. A custom inside size of 115 x 115 x 90 mm fits snugly. Before committing, check the external size against your carrier's price bands, and ask your supplier how a custom size compares with the nearest stock option.
If you ship two candles together, repeat the process for the pair. Multi-item boxes often justify a custom size.
Internal vs external
Suppliers usually quote mailer boxes by internal dimensions. External is roughly internal plus twice the board thickness on each axis, plus a little extra for the lid and any double walls. For E-flute (about 1.5 mm) that means adding about 3 mm or more to each measurement.
Carriers measure external, so when checking price bands use external. Ask your supplier for the external size of the exact box they quote, since construction details vary.
Board thickness
E-flute (about 1.5 mm) is a common choice for mailers up to around 300 mm: it prints well and folds crisply. B-flute (about 3 mm) is stronger and better for heavier contents or larger boxes, but it usually prints with slightly less fine detail. For very heavy items, ask about double-wall board.
Remember that the dieline changes with the board. Fold allowances for 3 mm board are different from 1.5 mm board, so settle the board with your supplier before artwork is final.
Shipping cost
Most carriers charge by the greater of actual weight and dimensional (volumetric) weight, which is length x width x height divided by a number the carrier sets. A box that is 20 mm larger than needed in each direction can push a parcel into the next price band.
Before you commit to a size, run the external dimensions through your carrier's calculator at your typical order weight. If you use more than one carrier, check each one, as their divisors and bands differ.
Weight matters too. Corrugated board adds weight, and so do inserts and filler. Weigh a packed sample on kitchen scales rather than estimating, then test both the weight and the external size against each carrier's rates.
Design implications
A bigger box has a bigger lid panel, which is your hero print area. A shallower box shows more of the inside of the lid when opened, which is where unboxing messages usually go. Side walls on a shallow box can be too narrow for anything but a logo or a short line.
In Packaroo you can set any inside dimensions for the mailer box and see your artwork on the 3D model, so you can judge the look at each size before you order samples. Check that your logo and key text still sit inside the safe area on every panel when you change the size.
Common sizing mistakes
- Measuring the product but not the extras. Inserts, cards, samples and filler all take space.
- Mixing internal and external. Quoting the product size as the box size, or checking carrier bands against internal dimensions.
- Too much room. The product slides around and needs extra filler, and the box can crush in transit.
- Ignoring the stack. If boxes are stored or shipped in cartons, a few millimetres can change how many fit.
- Skipping the sample. Measurements on paper rarely capture how a product sits in a real box.
Before you order samples
- Product measured at its widest points, with every item that goes in the box.
- Protection allowance added on each side.
- Internal dimensions written down and labelled as internal.
- External dimensions confirmed with the supplier and checked against your carrier's price bands.
- Board type agreed with the supplier.
- Artwork checked on every panel at the final size.
Then ask for a plain sample to test the fit with the real product before you approve a printed run.
Short answers
Should I pick one size for all my products? One size simplifies ordering and storage, but it can mean shipping air with your smaller products. Many brands settle on two or three sizes that cover most orders.
Do inches or millimetres matter? Use whatever your supplier uses, and always write the unit. Converting rounded inch sizes to millimetres (or back) can introduce small errors, so give the exact figure you want.
How much space is too much? If the product moves when you shake the closed box, there is too much space or not enough filler. Aim for a snug fit with your chosen protection.
Can I print inside the box? Usually yes, as an extra print side. It adds cost, so ask for a quote with and without inside print and decide whether the unboxing moment is worth it for your brand.
Will a heavier product need a different board? Possibly. Tell your supplier the packed weight and how the box will travel, and let them recommend a board.
Next step
Open the mailer box in Packaroo, type your internal dimensions and design on the dieline with a live 3D preview. You can start on the free plan. When you are happy, export a spec pack for A$15 with the dieline at 1:1 scale, the artwork PDF, renders and a specification sheet to send to suppliers. Related guide: What is a packaging spec sheet.