Example scenario · illustrative, not a real seller
The example bag contains a recognizable vehicle and a printed instruction cover. The wheels match the picture, but several distinctive pieces and a minifigure are absent. Identify and count before calling it complete.
What you’ll get
- Use official set and piece resources correctly.
- Distinguish a set, an incomplete build and a loose lot.
- Budget sorting and replacement research as active work.
- What LEGO’s set, element and design numbers each identify.
- A four-way offer table: complete set, incomplete set, loose lot or parted out.
Identify the set from its own numbers
A bag of used LEGO is one of the most tempting finds in reselling. You can see a wheel, a printed tile and part of an instruction booklet, and a quick search shows the complete set selling well. The gap between "a bag that contains some of a set" and "a complete set" is where both the profit and the disappointment live, and it is measured in pieces.
Start with the numbers LEGO itself uses. LEGO's official guidance on identifying sets and pieces distinguishes three kinds of numbers:
| Number | Where you find it | What it identifies |
|---|---|---|
| Set number | Box, instruction booklet cover | The set as sold |
| Element number | Listed in the back of the instructions for newer sets | A unique number for each piece |
| Design number | Molded small on the inside of many pieces | The shape; with the color, a way to identify a piece |
Use the set number to find the correct official building instructions on LEGO's instructions page. A design number helps you research a piece but does not, on its own, establish its color or which set it came from. Treat all of these as research clues, not a certificate for a mixed bag.
Keep brand names descriptive. Do not imply that you, or this site, are affiliated with LEGO or have officially inspected anything.
Sort before you count
Counting a mixed bag piece by piece against a booklet is slow. Sorting first makes it faster and more accurate:
- Separate obvious non-LEGO bricks and anything from other brands. Note them; do not mix them into the set.
- Pull out minifigures and printed or stickered parts, which are often the most important to the set's identity.
- Sort the rest by color, then by size or shape within each color.
- Set aside pieces that look like they belong to other sets.
Inspect as you go. Note cracked pieces, heavy scratches, discolored or yellowed parts, teeth marks and pieces with weak clutch power. Record anything damaged so you can disclose or replace it.
Inventory the actual contents against the set
Work through the official instructions step by step, or through a parts inventory for that set number, and check off each piece. Keep a running list of three kinds of gaps:
- Missing pieces.
- Substituted pieces: the right shape in the wrong color, or a similar piece from another set.
- Damaged pieces that are present but should be disclosed.
A nearly finished model can still be missing pieces central to its identity or function. A missing minifigure or a unique printed piece usually matters more to a buyer than a missing common plate.
Worked example: sorting consumes 75 minutes
Choose 15 minutes to identify the set and find its instructions, 45 to sort and inventory and 15 to photograph the contents and write missing-parts notes. That is 75 active minutes for one set.
| Task | Chosen minutes |
|---|---|
| Identify set and instructions | 15 |
| Sort and inventory | 45 |
| Photograph and note missing contents | 15 |
| Total active preparation | 75 |
If the inventory reveals missing parts you cannot replace, that time still happened even if no complete-set listing follows. A hypothetical $12 replacement-parts estimate should stay uncommitted until you have confirmed the exact elements, their price and their availability. Do not assume every missing minifigure or licensed piece is available from the same source, and do not use a new-set missing-parts service for used resale inventory in ways its terms do not allow.
Choose the truthful offer type
Once the count is done, decide which product you actually have:
| Offer | When it fits | How to describe it |
|---|---|---|
| Complete set | Every piece counted present, including minifigures | "Complete per official instructions; instructions included / not included" |
| Incomplete set | Most pieces present, gaps listed | "Missing the following pieces..." with the list |
| Loose lot | Mixed or unidentified contents | Describe by weight, piece count estimate or contents, without a set claim |
| Parted out | Valuable pieces sold separately | Each listing describes the actual part |
State whether the box and instructions are included. Do not use a photograph of the complete reference model as though it shows the contents you will send; photograph your own pieces, built or laid out.
Pack it and run the numbers
Bag the set in clearly labeled bags, ideally by instruction section or color, and pack the bags in a box with cushioning. Include the instructions flat so they do not crease. If you are shipping a built model, consider partial disassembly and say so in the listing.
Check CPSC's resale guidance too: its rules apply to anyone selling consumer products, and LEGO sets contain small parts, so keep any original age warnings intact. Then run your numbers through the lot reality tool, counting only the sets and parts you have verified. The minifigures guide covers figures in more detail.
Common mistakes to avoid:
- Calling a set "complete" because the build looks finished.
- Including third-party bricks without saying so.
- Photographing the box art instead of your actual pieces.
- Ignoring the time a mixed bag takes to sort.
A recognizable build is the start of an inventory, not the end of one. Let the count determine the description before the hoped-for complete-set price affects your decision.
Worked example · hypothetical, not a real seller
Keep the example in view
| Chosen sorting plan | Minutes |
|---|---|
| Identify set and instructions | 15 |
| Sort and inventory | 45 |
| Photograph missing contents | 15 |
| Total active preparation | 75 |
Before the next transaction
With JavaScript and browser storage, only checked-step IDs can stay on this device. No buyer details or amounts are saved.
Practical questions
Does a matching set number prove the bag is complete?
No. It identifies the reference set, not the actual contents. Count against the appropriate instructions or inventory.
Can I assume LEGO will replace used-lot missing pieces free?
No. Check actual availability, price and service eligibility. Do not misuse a new-set missing-parts process for resale inventory.
Where do I find LEGO element numbers?
LEGO says element numbers for newer sets are listed in the back of the building instructions, and many pieces also have a small design number molded on the inside.
How should I list a set with a few missing pieces?
As an incomplete set, with a list of the missing, substituted and damaged pieces, and whether the instructions and box are included.
Do this next · one concrete move