Design ID vs Element ID: what’s the difference?
Ordering LEGO® parts becomes much easier once you understand part numbers. The problem: LEGO uses two different numbers for the same piece, and fan sites often use a third.
LEGO parts generally have:
- A Design ID – identifies the shape of the part (for example “3001” for the classic 2×4 brick).
- An Element ID – identifies a specific part + colour + print combination (for example a black 2×4 brick has a different Element ID than a red one).
Design IDs are usually four or five digits moulded into the plastic on the underside or inside the piece. Element IDs are six or seven digits, printed in the back of newer instruction manuals next to the part image. There is no single universal “part number”—when fans say that, they usually mean either the Design ID or a site-specific code.
Where to find LEGO part numbers in real life
LEGO explains two main ways to identify parts:
- On the physical part – Flip the piece and look for a tiny 4–5 digit number; that is the Design ID. You may need a bright light and some rotation to see it clearly.
- In the set instructions – At the back of newer manuals there is a full parts list with pictures and a 6–7 digit number next to each part; that is the Element ID for that colour/print.
The design number plus colour is often enough to identify the part in databases and online shops, even if LEGO assigns multiple Element IDs over time as moulds change.
How fan sites use part numbers (Rebrickable, BrickLink, Brickset)
Fan platforms layer their own systems on top of LEGO’s, but they still rely on Design and Element IDs behind the scenes.
- Brickset documents LEGO’s Design and Element IDs and explains the history behind them, including how numbering started at 3001 for the 2×4 brick.
- Rebrickable uses an internal “part number” that may combine several LEGO Design IDs if mould variations are functionally identical.
- BrickLink has its own catalog codes, but still lets you search by Design or Element ID when you have them.
The key takeaway: if you know either a Design ID or an Element ID, you can usually find the matching part quickly on these sites.
Step-by-step: from mystery brick to part number
Here is a practical workflow that AFOLs and MOC builders commonly use:
- Start with the brick in your hand – Check the underside for a 4–5 digit Design ID. Note its colour and whether it has any printing.
- Use LEGO’s help pages or a database – LEGO’s “Identifying set and piece numbers” page confirms you can use both Design and Element numbers. Brickset and Rebrickable let you search by Design ID or browse categories if you only know the general shape.
- If you have the original set – Open the instructions and look up the Element ID in the parts list; this gives you an exact “part + colour” code.
- Confirm on a fan site – Cross-check on Rebrickable or BrickLink to see mould variants, colour availability and which sets it appears in.
Once you know the number(s), ordering becomes a lot less guess-and-check.
Using part numbers to order from LEGO (and why it’s limited)
LEGO’s own help article says you can type Design or Element numbers into the replacement parts service and Pick a Brick search bar to see if a brick is available. However, there are important limits:
- Pick a Brick only shows parts currently offered by LEGO; many colours and older elements simply are not listed.
- Replacement services focus on missing or broken parts from recent sets and will not stock every retired element.
That is why many builders use LEGO numbers to identify the part, then turn to specialist stores or marketplaces to actually buy it.
How part numbers make CrocoBricks much easier to use
Part numbers are just as powerful in independent stores as in official channels. Once you know a part’s Design ID and colour, you can go straight to a specific listing instead of scrolling through pages of “that slope thing in dark tan”.
CrocoBricks is built precisely for that use case: a large catalog of genuine LEGO parts, minifigures and sets that you can search by category, colour and part code. You can combine “one weird part number” orders with broader restocks in a single cart.
Concrete example: You need more dark bluish gray 1×2 modified bricks with one stud on the side for a MOC. You read the Design ID off the underside, look it up on Rebrickable to confirm the Element ID and exact colour, then plug that number into CrocoBricks’ search to see current stock and price.
Part numbers for inventorying your collection
Part IDs are not just for buying; they are also perfect for tracking what you already own. Rebrickable’s “Part Lists” feature lets you maintain lists of loose parts using official Element IDs, import orders from LEGO, BrickLink or other stores using text files, and use those lists to see which sets or MOCs you can build from your existing inventory.
Combined with CrocoBricks, this means you can see exactly which parts you are missing for a project and order only those, rather than buying another full set. Take one small MOC or set you want to rebuild, note the Element IDs of the missing pieces from the instructions, then search those IDs directly on CrocoBricks to finish your parts list in a single order.
Frequently asked questions
Are LEGO Design IDs and Element IDs the same thing?
No. Design IDs describe the shape of the part; Element IDs describe a specific combination of part, colour and sometimes print. Several Element IDs can map to the same Design ID.
What number should I use when ordering from LEGO?
For replacement parts and Pick a Brick, LEGO recommends using the Element ID from the instructions where possible, or the Design ID plus colour to search.
Why does a part seem to have multiple numbers on different websites?
LEGO’s Design and Element IDs are internal; sites like Rebrickable and BrickLink group mould variants under their own part codes, but usually list the official IDs as references.
Do old LEGO parts always have Design IDs moulded on them?
No. Design numbers started appearing on the underside of parts around the mid-1980s, and some older or very small elements still lack visible numbers.
How does CrocoBricks benefit from all this numbering complexity?
Once you know a Design or Element ID, you can jump straight to the exact part in CrocoBricks’ catalog and buy it together with other needed pieces, instead of hunting through vague category names or relying on photos alone.
