A parcel locker box should never be selected only by asking: “Will it fit into the locker?” For e-commerce teams, the real question is broader: will the final packed parcel fit the carrier limit, protect the product, stay fast to pack, reduce void fill and keep the shipping cost under control?
The best parcel locker packaging combines three things: correct external dimensions, product stability and a construction that works smoothly at the packing station. If you ship repeatable volumes, parcel locker boxes should be designed around real SKUs and shopping baskets rather than purchased as random stock sizes.
Quick answer: what are parcel locker size tiers A/B/C?
For InPost parcel lockers in Poland, the commonly used parcel size limits are:
| Size tier | Maximum parcel dimensions | Maximum weight | Typical e-commerce use cases |
|---|---|---|---|
| XS | 4 × 23 × 40 cm | 3 kg | very small accessories, documents, spare parts; service availability may vary |
| A | 8 × 38 × 64 cm | 25 kg | books, flat apparel, small sets, low-profile cosmetics |
| B | 19 × 38 × 64 cm | 25 kg | footwear, apparel, cosmetics, small electronics, product bundles |
| C | 41 × 38 × 64 cm | 25 kg | larger products, multi-item orders, products requiring more cushioning |
The important detail is that these are external dimensions of the final parcel, not the internal dimensions of the box. Corrugated board thickness, closure, tape, labels and any bulging after packing all count. For repeatable box design, leave a practical safety margin, especially on height.
If you need a broader overview of shipping cartons, see our guide to shipping boxes and courier cartons. This article focuses on parcel locker compatible boxes and size tiers A, B and C.
Size tier A: when does a low parcel locker box make sense?
Size tier A is the most demanding because the height limit is only 8 cm. It works best for flat, light and relatively robust products: books, catalogs, flat kits, accessories, folded apparel and small cosmetics held securely in place.
The main risk with A-size boxes is not length or width. It is final height after the product has been inserted and the box has been closed. A pack may look compliant on the table but exceed the limit once flaps, adhesive strips, labels or slight bulging are included. Always measure the final packed parcel, not the empty box.
Low die-cut boxes often work well because they close consistently and can reduce the amount of tape needed. For light products, lower flutes such as E or F may help keep wall thickness and external size down. For heavier products or sharp edges, board selection should be verified through testing rather than based on appearance alone.
A-size parcel locker boxes are a poor choice when the product has to be forced inside or when the box bulges after closing. Any saving on the shipping tier may quickly turn into operational friction, failed measurement, product pressure or a poor customer experience.
Size tier B: the practical standard for many online stores
Size tier B is often the most useful option for e-commerce because it gives significantly more height while still keeping the parcel compact. It works well for apparel, shoes, cosmetics, home accessories, small electronics and promotional bundles.
This is where standardization pays off. Instead of using one “B-size box for everything”, many stores benefit from 2-4 formats within the same size tier: lower, medium, higher and insert-ready. That way operators do not need to compensate for empty space with loose fill, and the business does not pay to ship air.
A B-size parcel locker box should be designed for repeatable closure. If the same product sometimes fits the size tier and sometimes does not, the issue may be box construction, too much void fill, insufficient safety margin or missing packing instructions. At scale, create a simple station-level SOP: which product goes into which format, how to position inserts, where to apply labels and when to move to size tier C.
Size tier C: more space, more responsibility
Size tier C gives the most height, but it should not become the default option “just in case”. Larger boxes often mean more empty space, higher risk of product movement and unnecessary shipping cost. A C-size box makes sense when the product truly needs volume, cushioning or stronger stabilization.
As boxes get larger, compression and puncture resistance matter more. Depending on product weight, transport route and stacking conditions, the packaging may need stronger corrugated board, a double-wall structure or a design that reinforces corners, bottom and closure areas. A bigger box does not automatically mean better protection.
In C-size packaging, product immobilization is critical. If the product can build momentum inside the box, it can hit the walls during sorting or handling. Loose void fill is not always the answer. Inserts, dividers, spacers, separators or a die-cut construction that holds the product in place are often more reliable.
How to choose a parcel locker box step by step
1. Start with products and baskets, not a box catalog
Collect your top SKUs and top shopping baskets. Mark flat products, fragile items, heavy goods, scratch-sensitive items, liquids and products frequently returned by customers. Only then can you see how many box formats are actually needed.
2. Measure the parcel exactly as it will be shipped
Do not measure the product alone. Measure the final parcel: product, protection, box, tape or adhesive strip, label and real closure. This is especially important for A-size boxes, where every millimeter of height matters.
3. Match the construction to packing speed
Regular flap boxes are versatile, but at higher volumes, die-cut boxes may reduce tape, shorten packing time and improve repeatability. If the customer is expected to return the product, consider a tear strip, adhesive strip and second closure from the start. We cover this in more detail in return packaging for e-commerce.
4. Select flute and board grade based on real loads
The corrugated board should match the product and the delivery chain. Lightweight apparel, glass cosmetics and electronics all create different risks. At BART, material and packaging decisions can be supported with tests for paper, corrugated board and finished boxes, including ECT, FCT and BCT. See Research and Technology and our corrugated board offer.
5. Leave margin for the real process
Designing a box right on the limit is risky. Corrugated board has tolerances, product dimensions vary, and operators may use different amounts of protection. A small practical margin is usually safer than dealing with parcels that only sometimes pass the carrier size tier.
6. Test packing at the workstation
A good test covers packing time, tape use, void fill, label placement, product stability and external dimensions after closure. If the box will be used in a fulfillment center, also check storage, picking and fast labeling.
Common mistakes with parcel locker boxes
The first mistake is confusing internal and external dimensions. A product may fit inside a box, while the packed parcel exceeds the carrier limit.
The second mistake is choosing a box that is too large and compensating with void fill. This increases cost, slows packing and creates more waste for the customer.
The third mistake is using board that is too weak for the actual product risk. A cheaper box can increase damage, returns and complaints.
The fourth mistake is missing operator instructions. Without a clear SOP, the same product may be packed in different boxes and the parcel cost becomes hard to control.
The fifth mistake is treating parcel lockers as a separate topic. Parcel locker boxes should fit the wider e-commerce model: courier shipping, fulfillment and returns. See the broader guide to e-commerce packaging.
When should you order custom parcel locker boxes?
Custom design makes sense when you ship repeatable volume, have dominant shopping baskets, see too much empty space or sell products prone to damage. The goal is not simply a better-looking box. The goal is a lower total parcel cost: less void fill, faster packing, better size-tier control and fewer complaints.
If you want to standardize parcel locker packaging, start with an audit. BART can review current formats, shopping baskets, packing process and transport risks, then propose a set of box formats based on data. See our packaging audit or go directly to packaging solutions.
FAQ
How do you choose a parcel locker box?
Measure the product with protection, select the size tier based on the external dimensions of the final parcel, leave a safety margin and test the packed parcel at the workstation. Then select flute, board grade and the final set of formats.
What box works best for parcel locker size A?
A low, repeatable die-cut or flap box works best for flat products. Height after closure must be controlled carefully because the A-size limit is tight.
Is parcel locker size B the most universal option?
For many stores, yes. But it should not be the only format. Several B-compatible box sizes can reduce empty space and void fill.
When should you use parcel locker size C?
Use size C for larger products, multi-item orders or products that need more cushioning. Product stabilization and board strength become especially important.
Can parcel locker packaging be more sustainable?
Yes. The biggest impact usually comes from right-sizing: less empty space, less void fill, optimized corrugated board and easier recycling. See our article on reducing void fill in e-commerce parcels.
