Mailer Box Sizes for D2C Brands: How to Pick the Right One
Measure your packed product, add 5 to 10 mm of clearance per side, and give that internal size to your supplier. Keep the box shallow so it fits through the letterbox of your courier's volumetric maths. When in doubt, order a sample first and check the fit against your real product.
How do I choose a mailer box size?
Measure your packed product at its widest, longest and tallest points, then add 5 to 10 mm of clearance per side. That packed measurement plus clearance is your internal size. Keep the height as low as the product allows, because height drives both the fit and the courier bill. Give that internal size to your supplier, not the outside of the box.
The clearance matters. Too tight and the product fights the lock every time your packer closes the box. Too loose and it slides, so you add void fill and the parcel bills heavier on the courier scale. A snug 5 to 10 mm gap per side is the sweet spot for most D2C goods: apparel, cosmetics, small tech, subscription kits and gifting.
Mailers run in E flute for a slim premium wall or B flute when the contents need more cushion. Any internal dimension you send can be cut, from 500 pieces per size. The size table below is a starting point by product type, not a rule. Your real product weight and courier route decide the edge cases.
| Product type | Internal size (mm) | Flute |
|---|---|---|
| Jewellery, small accessories | 120 x 100 x 40 | E flute |
| Cosmetics, skincare set | 180 x 140 x 60 | E flute |
| Folded apparel, single tee | 250 x 200 x 80 | E or B flute |
| Subscription kit, multi-item | 300 x 220 x 100 | B flute |
| Gifting, hamper, heavier bundle | 350 x 280 x 120 | B flute |
These are typical footprints, not fixed SKUs. If your product sits between two rows, size to the product and not to the nearest stock box. That is the whole point of a made-to-size mailer: the box fits what you sell. Share your size on WhatsApp for a quote.
Internal vs external dimensions: which do I give my supplier?
Always give internal dimensions. Internal size is the clear space your product sits in; external size is that plus the board thickness on every wall. Your supplier cuts to internal size so the product fits. If you send external numbers by mistake, the usable space shrinks by the board on all sides and the product may not go in.
The gap between the two grows with ply and flute. A single wall E flute mailer adds roughly 1.5 mm per wall, so external is a few millimetres bigger than internal on each axis. B flute adds more. This is small on one box and real across a pallet, which is why the industry quotes internal size as the standard.
Give your supplier internal dimensions. That is the clear space your product sits in, not the outside of the box.
- Internal size: the clear inside space, measured product plus 5 to 10 mm clearance per side.
- External size: internal plus board thickness on every wall, which grows with flute and ply.
- Quote and order on internal size, so the fit is guaranteed against your product.
- Use external size only to plan warehouse shelf space and master-carton packing.
- State the unit every time. The quote engine takes inches or millimetres, so there is no guessing.
One saved spec carries your internal dimensions, ply and print, so every reorder matches the first one exactly. You never re-measure or re-argue the size once a sample is signed off. Share your size on WhatsApp for a quote.
How does box size affect courier charges?
Indian couriers bill the greater of actual weight and volumetric weight. Volumetric weight is length times width times height in centimetres, divided by 5000. That divisor applies to standard domestic courier. A light product in a tall or oversized mailer bills on the box, not the product, so size drives the freight bill on every single parcel.
Reduce height first. Height multiplies straight into the volume, so a mailer cut close to a folded garment bills lighter than a deep carton holding the same item. The table below runs the divisor 5000 on three mailer footprints. Sizes are in centimetres and the billed figure is the greater of actual and volumetric weight.
| Mailer size (cm) | Actual kg | Volumetric kg | Billed kg |
|---|---|---|---|
| 25 x 20 x 8 | 0.50 | 0.80 | 0.80 (volumetric) |
| 25 x 20 x 5 | 0.50 | 0.50 | 0.50 (equal) |
| 30 x 22 x 10 | 0.70 | 1.32 | 1.32 (volumetric) |
Look at the first two rows: same footprint, 3 cm less height, and the billed weight drops from 0.80 kg to 0.50 kg on the same product. That saving repeats on every order for the life of the SKU. This is why a shallow, snug mailer is not only a nicer open, it is a cheaper parcel. Check each SKU once with L times W times H in cm divided by 5000, and store the number.
A mailer cut 3 cm shallower can drop the billed weight on every parcel for the life of the product.
Mailer box or RSC shipper: which should I use?
Pick a mailer for light, flat, premium products up to about a kilo where the open is part of the brand. Pick an RSC shipping box for heavier, bulkier or fragile items that need 5-ply strength and internal fitment. The size logic is the same for both: measure the packed product, add clearance, order on internal dimensions.
A mailer is a self-locking box with a roll-end front tuck. It ships flat, closes without tape, and opens into a clean tray, which is why brands use it for the unboxing. An RSC is a Regular Slotted Carton: four flaps taped top and bottom, built to protect a heavier load in bulk. Many brands run both, a mailer for the hero single-product order and an RSC range for multi-item carts.
When you are close between the two, order a sample of both and test them with your real product before you commit a full run. You approve a physical sample first either way, so you hold the box, close the lock, and check the fit before any production starts. Only after that sample is signed off does production run in NCR and dispatch pan-India with tracking and a GST invoice. Share your size on WhatsApp for a quote.
Frequently asked questions
What size mailer box do I need?
Measure your packed product at its longest, widest and tallest points, then add 5 to 10 mm of clearance per side. That internal size is what you order. Keep the height as low as the product allows, because height drives both the fit and the courier volumetric weight. Share your size on WhatsApp for a quote.
Do I give internal or external dimensions?
Internal, always. Internal size is the clear space your product sits in; external is that plus the board thickness on every wall. Suppliers cut to internal size so the fit is guaranteed. Use external size only to plan shelf space and master-carton packing, never to order the box itself.
Does a smaller mailer really cut courier cost?
Yes, when the parcel bills on volumetric weight. That figure is length times width times height in centimetres divided by 5000 for standard courier. Trimming height and clearance lowers the volume, which lowers the billed kilograms. Cutting a few centimetres off the height can drop the billed weight on every shipment of that SKU.
What is the smallest order I can place?
Mailers start at 500 pieces per size, in any internal dimension you send. Smaller pilot runs are possible for a new brand testing a size, so ask on WhatsApp. You approve a physical sample before any full run, so you confirm the fit and the lock against your real product first.