Calibron 12 - Theodore Edison's 1933 Wooden Packing Puzzle

Calibron 12 is a wooden packing puzzle designed in 1933 by Theodore Miller Edison, the youngest son of Thomas Edison, an MIT-trained physicist who held more than 80 U.S. patents and founded Calibron Industries in West Orange, New Jersey. We build this faithful reproduction at Creative Crafthouse, our family-owned wooden puzzle and game shop, and make every set in our Hudson, Florida workshop.

The goal is to arrange twelve wooden pieces into a single square, and only one arrangement works. The original 1933 wording ships with every set and is deliberately misleading: arrange the twelve blocks to form a single large rectangle. Any rectangle, including the square, will do, provided every block is used. In practice only one solution exists, and it is the square. Calibron 12 anchors our Impossible Puzzle Series, carries our 11 out of 10 difficulty rating, and is widely considered one of the hardest wooden packing puzzles ever designed. Most solvers work at it for days or weeks, and some never finish.

Each piece is laser-cut from ash, maple, walnut, and other fine woods, with its dimensions engraved into the wood so the markings will not rub off with handling. The assembled tray measures 9.5 by 7.5 by 0.75 inches, a substantial desk-sized piece rather than a pocket puzzle. The set includes the wooden tray base, all twelve pieces, a fitted wood cover, and a printed solution sheet for when you have exhausted every other idea. It ships unsolved. Standard orders ship in one business day and personalized orders in two.

We laser-engrave the wood cover with a name, a date, or a short message, up to 45 characters, so the puzzle can double as a keepsake. It is a favorite gift for engineers, mathematicians, puzzle collectors, STEM teachers, and dads who want a challenge that lasts longer than an afternoon.

Recognition. Calibron 12 was the subject of The Mystery of the Calibron Twelve Block Puzzle, a research paper by George Miller and Nick Baxter presented at the Gathering 4 Gardner G4G12 conference in Atlanta, 2016. The paper traces Theodore Edison's original 1933 design and the rediscovery of its precise piece dimensions, and documents that Edison issued the original in three versions, identical in their twelve pieces but each packed with a differently sized black spacer so the closed box never revealed the solution. David Janelle of our Hudson, Florida workshop is named in the paper's acknowledgements. Read the paper.

Want another puzzle at this level? Try the Einstone II, or browse the full Impossible Puzzle Series.

Designed by Theodore Edison, 1933. Handcrafted today by Creative Crafthouse in Hudson, Florida.