Size a mailer box around the largest assortment you actually plan to ship. Measure the products with their caps, wraps, or sleeves in place, then account for the divider and any card. Check the finished outside dimensions separately. The space your products need and the size of the parcel are two different numbers.
Start with two real packing layouts
Imagine a tea subscription with two small tins and a sealed sample sachet. Most months, the same tins go into the left and right lanes, with the sachet between them. In a seasonal month, one tin gets a taller lid. Lay out both versions with the card in its actual position before you choose from standard mailer box sizes or ask for a custom size.
For this layout, a one-piece corrugated mailer with an attached lid and side locking ears gives the subscriber a clear first view. Of the mailer box inserts you could try, a fitted three-lane divider is a simple starting point. It keeps the tins apart and gives the sachet a dedicated spot. Check what happens if a tin can slide along its lane or tip forward when the box is turned. A divider can separate items while still leaving room for them to move.
Ask for three measurements on the sample
- Usable interior. Fit the divider and products before you judge the available space. Include the lid’s tuck flap where it folds into the box.
- Clear height under the closed lid. Close the sample with the tallest tin and the card inside. Check for contact marks, a raised lid, or a front flap that needs extra force to lock.
- Finished outside dimensions. Measure the closed, fully packed sample at its widest points. Give those dimensions to your fulfillment team or carrier for a shipping estimate.
Keep one box size if the monthly changes are small
For a shorter seasonal tin, try a revised divider or a folded paperboard spacer in that lane. If the taller assortment needs a bigger shell and the regular one still shifts after you adjust the insert, get a second size quoted. If you are comparing custom corrugated boxes from different suppliers, give each one the same packed layouts and quantities. Compare the outside dimensions and the time it takes to pack each option.
Pack a few samples the way your team will on a normal day, including the label and any sealing tape. Check how easily they close, how the contents move when you turn the packed box, and whether the first view still looks tidy when reopened. If the same box will go straight through parcel delivery, test the complete packed configuration before ordering in bulk.
Can the same mailer box work without a divider?
It can work for an assortment that stays in place once packed. For two round tins and a loose sachet, start with a divider. Pack one sample each way and compare movement, setup time, and what the customer sees when the lid opens.
Related packaging options
Explore custom mailer boxes and paperboard and corrugated insert options. See ecommerce and subscription packaging if you are planning several assortments.
Get a mailer box quote. Send the regular and largest layouts, product dimensions, packed weight, order quantity, and delivery ZIP code.