1 Check the bags and the spare pieces
In many LEGO® sets, the pieces are split into bags numbered after the steps of the building instructions. Before deciding a piece is missing, open the remaining bags and look at the bottom of the box.
Some sets also include a few spare small pieces. Look at what is left on the table: the piece you are after may be there.
2 List exactly what is missing
A LEGO® piece is defined by two things: its part number (its shape) and its color. “A gray brick” is not enough to find it, let alone to order it.
With BrickBack, add the set by its number, the one printed on the box and the instructions: the app loads its complete set contents, piece by piece and color by color, from over 28,000 sets. Check off what you have; what remains is the list of missing pieces, with each piece's part number in the instructions where one exists.
3 Search the loose bricks
A stray piece may have slipped into another set's tub, among pieces that look like it.
Scan a piece with BrickBack: the app identifies its name and color, then shows the sets in your collection that are missing it. Check it off for one of them: the missing count goes down and progress goes up. “− 1 +” adjusts the quantity, up to the number still missing. Scanning is free and unlimited.
4 Identify an unknown piece
Some pieces carry a tiny molded number: it is the part number of their shape. It does not give the color, and it can be unreadable or absent. If you can read it, “Search for a piece” looks the piece up in BrickBack by that number, with no photo; the search also takes its name and its color.
A photo is the other way: BrickBack sends the image to Brickognize, an online recognition service. Scanning needs a connection and your consent before the first photo. “Cancel” stops the wait; if the service does not respond, “Try Again” retries with the same photo.
The picture shows the piece in the selected color; “Other colors” opens its other colors. The part number from the instructions is shown when available, with other numbers and explanations behind ⓘ. “Double-sided” marks minifigure heads printed with a second expression.
5 Replace it, in the right place
- A new set, incomplete out of the box: the manufacturer replaces missing pieces from a new set free of charge, when the box is opened. For a recent enough set, BrickBack opens the page of that service.
- An older or second-hand set: the manufacturer's single-piece shop, or the spare-parts marketplaces. Whether a piece is offered in a given color depends on what was produced and what is still in stock.
BrickBack opens the manufacturer's single-piece shop on that set's pieces. “Pieces to buy”, in the “To buy” tab, gathers the missing pieces from all your sets in one list that stays up to date. The list, excluding pieces already in your loose bricks, and its spreadsheet (CSV) or Rebrickable exports are free. File exports of your collection, wishes and loose bricks remain Pro.
Pro adds printing, filtering by set, choosing the order, and BrickLink or Brick Owl exports, which you import yourself on those sites. BrickBack does not show part prices and places no orders: the price and the purchase are the merchant's.