When opening a new box, most of the pieces are in closed plastic bags, and sometimes inside those plastic bags is another plastic bag for smaller pieces.

I find the pieces, for the most part, rather random. Sometimes a particular brick shows up in more than one bag.

It seems like an odd way to make sure all of the pieces are there in the box, and yet, a box is rarely, if ever, missing a brick.

Any rhyme or reason to how Lego packages the pieces for a new set?

  • 1
    "Sometimes a particular brick shows up in more than one bag." Perhaps that particular brick is used in more than one model (if the set features multiple models together)? Commented Nov 1, 2011 at 19:28

4 Answers 4


The goals for packaging are most likely efficiency and dependability. I would think LEGO's interest is to achieve this using an automated process. This explains why a missing piece is a very rare event.

  • Size concerns: Similar piece volume in each bags.
  • Sub packaging symmetry: Same bag used several time in a box.
  • QA is done by weighting bags. Extra (small) pieces are favored over the occasional missing piece.

Check this video on the lego plant automation.


The main goal is certainly packaging efficiency (possibly where parts come from in the factory, for example), but there are other factors coming in.

Sets which have "modular" building need to have numbered bags, and the numbering has prioity on other considerations — you'll need all bricks for module 1 to be in bags numbered "1" (plus sometimes, unbagged parts).

Also, elements which are too similar are usually in different bags. This helps finding them when building, but another reason for that might be the random checks which are done on bag contents during the packaging process, as I believe these are manual.

Sometimes, if an element is in huge quantity in a set, it can also get its own bag; and as jfyelle says, sometimes a same bag can appear twice in a set — it's easier for packaging than two bags with different contents.


This way of packaging is most likely optimized to prevent packaging errors. One of the leading method is the poka-yoke technique.

Poka-yoke is a technique for avoiding simple human error in the workplace.

By using jigs, automated(robotic) counting and other means this method aims to eliminate errors in a repetitive workflow.

  • "Something that applies to Lego could be to not have large numbers of the same piece together in the same bag." Given the bags I have seen this is utterly false. Lego packaging is mostly automated, and it can be checked to a very high degree of accuracy by weight.
    – user23
    Commented Nov 2, 2011 at 13:18
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    poka-yoke is not only for manual jobs but for automated systems (as stated in the page I linked to). I'll remove my last sentence since it assumes that Lego as some manual packaging. The rest is good I would be really surprised if they were not using an existing method like poka-yoke.
    – pcantin
    Commented Nov 2, 2011 at 13:26

Yes. In the instructions, you will see a big number 1 or 2. These numbers are also printed on the bags. So all the parts you need for section 1 will be in bag 1, all the parts for section 2 will be in bag 2, etc.

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