Pocket Cube
The Pocket Cube, also known as the 2×2×2 Rubik's Cube or Mini Cube, is a compact mechanical puzzle consisting of eight smaller corner cubies arranged in a 2×2×2 cubic structure, allowing rotations around three axes to scramble and solve its colored faces.[1] Invented in 1970 by American engineer Larry D. Nichols as a magnetic version of a rotatable group puzzle, it was patented in 1972 under U.S. Patent 3,655,201 for a "pattern forming puzzle" with pieces that twist in groups without fixed centers or edges.[2] Marketed by the Rubik's brand since 1981 as a portable entry-level challenge, the puzzle features six colored faces and exactly 3,674,160 possible positions, calculated as 7! × 3^6.[1] Unlike the larger 3×3×3 Rubik's Cube, the Pocket Cube lacks edge and center pieces, simplifying its mechanics while retaining the core challenge of aligning colors through layer turns, making it ideal for beginners or on-the-go solving.[1] The puzzle gained widespread popularity alongside the original Rubik's Cube, inspiring speedcubing events that use advanced methods like the Ortega or CLL algorithms.[3]Overview
Definition and Naming
The Pocket Cube is a 2×2×2 combination puzzle composed of eight smaller corner cubies that assemble into a larger cube-shaped toy, with each of the six faces featuring four stickers of the same color in its solved state.[1][4] As a twisty puzzle, it allows rotations of its outer layers by 90 degrees, enabling the cubies to be rearranged through a series of turns.[5] Typically measuring about 5 cm (50 mm) on each side, the Pocket Cube is notably smaller and more compact than larger variants in the Rubik's Cube family.[6] This diminutive size contributes to its alternative names, including Mini Cube and simply 2×2 Cube, with "Pocket Cube" specifically derived from its portability, allowing it to fit easily into a pocket or bag for on-the-go play.[1][7] The primary objective of the Pocket Cube is to scramble its colors through random turns and then restore it to the solved configuration, where each face displays a uniform solid color, providing an accessible introduction to twisty puzzle mechanics.[4] It serves as a simplified variant of the original Rubik's Cube family.[5]Relation to Rubik's Cube Family
The Pocket Cube belongs to the broader family of twisty puzzles marketed by the Rubik's brand as extensions of the original 3×3×3 Rubik's Cube invented by Hungarian architect Ernő Rubik in 1974.[8] This family encompasses various nxnxn cube variants, including the 2×2×2 Pocket Cube, the standard 3×3×3 cube, the 4×4×4 Rubik's Revenge with increased complexity from multiple edge pieces, and larger iterations like the 5×5×5 Professor's Cube.[7] These puzzles share a core philosophy of mechanical manipulation to rearrange colored facets, with the Pocket Cube serving as the simplest member due to its compact size and reduced complexity.[4] A primary distinction of the Pocket Cube from other family members, particularly the 3×3×3, lies in its construction: it features only 8 movable corner pieces with no fixed center pieces or dedicated edge pieces, resulting in a streamlined mechanism that eliminates the need to orient centers or resolve edge pairings.[4] In contrast, the 3×3×3 incorporates 20 movable pieces (8 corners and 12 edges) around 6 fixed centers, introducing additional layers of permutation challenges.[8] This minimalism makes the Pocket Cube physically smaller and easier to manipulate, often fitting in a pocket, while larger variants like the 4×4×4 amplify complexity through multiple identical edge pieces and movable centers.[7] Despite these differences, the Pocket Cube maintains fundamental similarities with its family counterparts, employing the same quarter-turn twisting mechanism along three orthogonal axes to rotate layers independently.[4] It adheres to the conventional six-color scheme—typically white, red, blue, orange, yellow, and green—applied to its faces, mirroring the visual goal of aligning solid colors on each side through permutation-based solving principles.[8] Within the cubing community, the Pocket Cube is commonly utilized as an introductory puzzle for newcomers intimidated by the full 3×3×3 and as a training tool for speedcubers honing finger dexterity and recognition speeds, given its manageable 3,674,160 possible configurations versus the 3×3×3's 43,252,003,274,489,856,000 positions.[9][8]History
Invention and Early Development
The Pocket Cube was invented in 1970 by American engineer Larry D. Nichols as a 2×2×2 puzzle with pieces rotatable in groups, held together using magnets.[2] Nichols filed a Canadian patent application in March 1970 and was granted U.S. Patent 3,655,201 on April 11, 1972, assigned to Moleculon Research Corp. Nichols' design explored rotational movements in a compact cubic structure, predating Ernő Rubik's work on larger cubes. Rubik developed his own version of the 2×2×2 puzzle as part of the Rubik's Cube family, but it was not the original invention. In 1982, Moleculon sued Ideal Toy Corporation for patent infringement regarding Rubik's Pocket Cube. The court ruled in 1984 that the 2×2×2 version infringed Nichols' patent, a decision affirmed on appeal in 1986; however, the 3×3×3 Rubik's Cube did not infringe.Commercialization and Popularity
Rubik's version of the Pocket Cube, branded as Rubik's Mini Cube, was released by Ideal Toy Corporation in 1981 following the success of the 3×3×3 Rubik's Cube, which had been licensed in 1979.[5] The Mini Cube was marketed as a portable, entry-level puzzle, appealing to consumers during the early 1980s Rubik's Cube craze.[10] Sales of Rubik's products, including the Mini Cube, contributed to over 100 million units sold worldwide by the mid-1980s, featured in media, advertisements, and toy lines.[11][12] The Pocket Cube gained cultural prominence alongside the original cube, appearing in educational tools and pop culture. A resurgence in popularity occurred in the 2000s, driven by online speedcubing communities that developed advanced techniques, positioning the 2×2×2 as an accessible starting point for competitions.[13] Modern versions are produced by brands such as QiYi and MoYu, offering performance-oriented designs with stickerless finishes for speedcubing.[14][15]Design and Mechanics
Physical Construction
The Pocket Cube is primarily constructed from ABS plastic, valued for its durability, impact resistance, and lightweight nature, ensuring the puzzle withstands repeated twisting without deformation. External surfaces feature colored stickers applied to the corner pieces or, in contemporary models, heat-transferred or molded plastic tiles for fade-resistant coloring that eliminates peeling issues.[16][17][18] Internally, the puzzle comprises eight corner cubies connected to a central core, typically a spherical black plastic mechanism, with integrated axles facilitating 90-degree rotations of the faces. This core design allows independent movement of each layer while maintaining structural integrity. Modern speedcube variants incorporate adjustable tensioning screws around the core to fine-tune rotation smoothness and speed, often incorporating magnetic elements for improved stability and alignment, enhancing performance for competitive solving.[19][20][21] Standard dimensions measure 50 to 57 mm per side, rendering the Pocket Cube highly portable, with weights ranging from 50 to 70 grams depending on the model and reinforcements. For instance, the official Rubik's 2x2 Speed Cube is 51 mm per side and weighs about 65 grams. Speedcube models often include rounded edges to reduce friction during turns.[22][23][24] Variants expand the standard design, such as picture cubes with photographic or custom images printed on the faces for thematic puzzles, super cubes featuring additional orientation markers on the corners to increase complexity beyond permutation alone, and DIY builds fabricated via 3D printing for personalized sizes, materials, or mechanisms. The Pocket Cube employs a similar ABS plastic construction to its larger 3x3x3 counterpart in the Rubik's family.[25][26]Piece Types and Movements
The Pocket Cube, also known as the 2×2×2 Rubik's Cube, is composed exclusively of eight corner pieces, each displaying three distinct colored stickers on its visible faces. These pieces are identical in structure and function, differing only in their color combinations, which correspond to the six faces of the cube. Each corner piece can adopt one of three possible orientations, determined by the alignment of its colors relative to the adjacent faces, allowing for rotational twists during solving.[4][27][28] Unlike larger cubes in the Rubik's family, the Pocket Cube lacks edge pieces and movable center pieces, reducing its mechanical complexity to solely the movement and positioning of these eight corners. The absence of centers and edges means the color scheme is defined relative to the puzzle's internal core, which remains fixed and orients the overall structure. This simplification results in constraints where only even permutations of the corner pieces are achievable, as odd permutations cannot be reached through legal moves due to the fixed reference provided by the core.[4][5][29] Movements on the Pocket Cube involve quarter turns of 90 degrees or half turns of 180 degrees applied to individual layers around the three principal axes: the x-axis (left-right), y-axis (up-down), and z-axis (front-back). Each such turn rotates one face layer independently, cyclically permuting four corner pieces in a 4-cycle while preserving the positions of the remaining four. These operations allow the layers to move freely without interference from edges or centers, enabling the cube to achieve its 3,674,160 possible configurations through sequences of these basic twists.[30][27][5] For optimal performance, particularly in speedcubing variants constructed from durable plastic, lubrication with silicone-based sprays or oils is commonly applied to reduce friction between the corner pieces and the core mechanism. Maintenance routines include disassembly, which is achieved by carefully prying apart the corner pieces from the central axis using a flat tool, followed by cleaning to remove dust and debris before re-lubricating and reassembling. This process ensures smooth, reliable turns over extended use.[31][32]Mathematical Foundations
Permutation Group Structure
The Pocket Cube group, denoted G, is the group generated by quarter-turn rotations of its six faces, acting on the configurations of its eight corner pieces. It acts via permutations in the symmetric group S_8 on the eight corners and orientations, with |G| = 3,674,160.[33] The structure of G decomposes into the permutations of the eight corners and the possible orientations of those corners. The permutation component consists of all possible permutations (order 8! = 40,320). Fixing one corner to establish a reference frame yields 7! = 5,040 permutations of the remaining corners.[33] The orientation component arises from each corner having three possible twists (0, 1, or 2 times 120 degrees), giving 3^7 = 2,187 possibilities overall under the total twist constraint (equivalent to 3^8 / 3), but fixing the reference corner's orientation yields 3^6 = 729.[33] Key rules govern the reachable states: the total orientation (sum of twists) must be a multiple of 3 (since each face turn twists corners by a total of 0 mod 3). Unlike larger cubes, there are no edges, so no edge permutation or flip parities; unlike the 3×3×3 cube, there is no even permutation constraint on corners (each face turn is an odd 4-cycle permutation).[33] G is a semidirect product of the corner permutation group S_8 acting on the corner orientation group (\mathbb{Z}/3\mathbb{Z})^7, incorporating the total twist constraint. This structure highlights the coupled nature of position and orientation changes under moves, with no separate edge handling required.[34]Total Number of Configurations
The total number of reachable configurations of the Pocket Cube is 3,674,160. This figure arises from the permutations and orientations of its eight corner pieces, subject to the puzzle's mechanical constraints. The formula is $8! \times 3^8 / (24 \times 3), where $8! represents the arrangements of the eight corners, $3^8 their possible orientations (three per corner), divided by 24 to account for the cube's rotational symmetries (the order of the rotation group), and by 3 because only configurations with total corner orientation summing to a multiple of 3 are reachable.[33] Equivalently, fixing one corner in a specific position and orientation to define the reference frame yields $7! \times 3^6 configurations: $7! ways to permute the remaining seven corners and $3^6 ways to orient six of them (with the seventh determined by the total twist constraint). This computes to $5,040 \times 729 = 3,674,160. Accounting for rotational symmetry, there are $3,674,160 / 24 = 153,090 distinct configurations up to whole-cube rotation.[33] In comparison, the 3×3×3 Rubik's Cube has approximately 43 quintillion ($4.3 \times 10^{19}) positions, orders of magnitude more due to additional edge and center pieces. The Pocket Cube's modest state space enables full enumeration by computer, facilitating exhaustive analysis. The God's number—the diameter of the configuration graph, or the worst-case minimum moves to solve any position—is 11 in the half-turn metric (where 180° turns count as one move) and 14 in the face-turn metric (where 90° and 180° turns each count as one). These bounds were established through computer-assisted exhaustive search of the state space.[35]Solving Approaches
Beginner Layer-by-Layer Method
The beginner layer-by-layer method for the Pocket Cube provides an accessible introduction to solving the puzzle by constructing it layer by layer, starting with the bottom face and progressing to the top. This approach emphasizes intuitive color matching for the initial layer and relies on a small set of basic algorithms for the upper layers, making it suitable for novices without requiring memorization of complex sequences. By design, the method proceeds in a way that maintains the parity of corner permutations, avoiding unexpected issues that could arise in more advanced techniques.[36] Step 1: Solve the first layerBegin by selecting one face color, typically white, to serve as the bottom layer. Identify the four corner pieces containing the white stickers and position them on the bottom face, ensuring each corner's adjacent side colors match the corresponding centers on the adjacent faces. This step is largely intuitive: hold the cube with the bottom face down, locate a white corner in the top layer, rotate the top layer to align it above its correct slot based on side colors, and turn the appropriate face to insert it. Repeat for all four corners until the entire bottom layer is solved, with white on the bottom and matching side colors around it. This process typically requires no algorithms beyond intuitive turns.[36] Step 2: Position the second layer corners
With the bottom layer fixed, turn the cube so the bottom remains oriented downward and focus on the top layer corners, positioning them relative to the solved bottom by matching their non-bottom colors to the adjacent sides. Rotate the top layer (U) to align unsolved top corners into their target positions based on the bottom layer's side colors, ignoring orientation for now. If corners are mismatched, use top layer turns to align pairs or apply a corner permutation algorithm such as U R U' R' U' F' U F (for adjacent swap) or R U2 R' U' R U' R' (for diagonal swap) to resolve the positions without disrupting the bottom layer. This effectively performs even permutations, ensuring all four top corners are positioned correctly. Only basic permutation sequences are needed here.[37] Step 3: Orient the last layer corners
Once the top corners are positioned, orient them so all top face colors (typically yellow) face upward. Hold the cube with the bottom layer down and an unsolved top corner in the front-right position. Apply a basic orientation algorithm such as the 4-move sequence (e.g., R U R' U') adjusted for the case, repeating as needed until the top color is correctly oriented, then rotate the top layer (U) to bring the next unsolved corner to the front-right without turning the whole cube. Proceed around the top layer until all corners are oriented, completing the solve. This step uses simple repetitive sequences, bringing the total to a few basic ones across the method.[36] Tips for success
Throughout the process, prioritize matching colors on adjacent faces to build intuition for piece relationships, and always hold the cube with the solved bottom layer facing down to prevent undoing previous work. Practice each step separately before combining them, using standard notation (R for right face clockwise, U for up face clockwise, etc.) to describe turns clearly. This method's layer-by-layer structure inherently avoids parity issues, as corner permutations remain even at each stage, allowing consistent solvability without additional fixes.[36]
Advanced and Optimal Algorithms
Advanced solving techniques for the Pocket Cube build upon beginner layer-by-layer approaches by emphasizing efficiency, recognition speed, and algorithmic memorization to achieve faster solve times. The Ortega method, also known as the Varasano method, involves solving the first layer using intuitive pairing of corners, followed by orienting the last layer corners (OLL) and permuting both layers (PBL) with a set of about 12 algorithms.[38] This method allows solvers to reach average times under 5 seconds with practice.[38] For even greater speed, the Corners of the Last Layer (CLL) method extends first-layer solving by applying one of 42 algorithms to simultaneously orient and permute the remaining four corners.[39] This reduces the last layer to a single step, eliminating separate OLL and PLL phases common in larger cubes, and enables expert averages below 10 seconds through rapid case recognition and execution.[40] Nine of these algorithms overlap with Ortega's PBL set, facilitating a smooth transition between methods.[40] Yau-inspired variants adapt corner-first strategies from larger cubes to the Pocket Cube's design, focusing on initial corner placement without edge pairing due to the absence of edges. These approaches emphasize solving opposite corners first, akin to Ortega's structure, before addressing the remaining four, often incorporating 2-look last layer techniques for efficiency. Experts using such methods achieve sub-10 second averages by leveraging intuitive corner building and minimal algorithm reliance. Optimal solving explores the Pocket Cube's theoretical limits, where computer algorithms generate solutions in at most 11 moves under the half-turn metric (HTM), known as God's number.[35] These solvers use exhaustive search within the cube's 3,674,160 positions to find minimal paths, often employing commutators for efficient 3-cycles of corners. Human solvers approximate optimality by incorporating commutator-based sequences to resolve 3-cycles, reducing move counts in practice.[41] Parity issues are inherently resolved in the Pocket Cube due to its permutation group structure, which consists solely of even permutations of the eight corners (isomorphic to the alternating group A8). Unlike the 3x3x3 cube, where edge and corner parities must align, the Pocket Cube avoids additional parity algorithms, as all reachable states maintain even permutation parity without OLL/PLL distinctions.[42]Notation System
Standard Face and Turn Notation
The standard notation system for describing turns on the Pocket Cube, developed by David Singmaster in 1979, assigns single uppercase letters to each of the six faces: U for up, D for down, F for front, B for back, L for left, and R for right.[43][44] This system allows precise communication of movements across the cubing community. A lone letter signifies a 90-degree clockwise quarter turn of the specified face, viewed as if looking directly at that face from outside the cube.[45] An apostrophe (') appended to the letter indicates a 90-degree counterclockwise turn, while the numeral 2 denotes a 180-degree half turn in either direction.[46] For the Pocket Cube, which lacks edge and center pieces, only these basic quarter and half turns apply, as there are no inner layers to necessitate wide or multi-layer moves.[47] Notation is interpreted relative to the solver's perspective, with the cube conventionally held so the up face is on top and the front face faces the solver; during solving, this often aligns the target solved color (typically white) on the up or down face.[47] For instance, the sequence R U R' consists of a clockwise right-face turn, followed by a clockwise up-face turn, and concluded by a counterclockwise right-face turn, effectively cycling three corner cubies in a basic permutation.[45] This notation underpins the representation of algorithms in Pocket Cube solving methods.[43]Algorithm Representation
In the representation of algorithms for the Pocket Cube, sequences of moves are written using standard Singmaster notation, where uppercase letters denote clockwise 90-degree turns of the corresponding face (U for up, D for down, L for left, R for right, F for front, B for back), a prime symbol (') indicates a counterclockwise 90-degree turn (e.g., U'), and the numeral 2 signifies a 180-degree turn (e.g., U2).[45] Spaces between moves are optional and primarily used for readability in longer sequences, allowing solvers to parse algorithms efficiently without altering their execution.[48] This format enables the concise documentation of solving steps or scrambles, applicable directly to the 2x2x2 structure since all turns affect the outer layers exclusively. Commutator notation provides a compact way to express sequences that achieve specific permutations, such as 3-cycles of corners, which are central to advanced Pocket Cube solving. A commutator is denoted as [A:B], expanding to A B A' B', where A and B are subsequences of moves, and A' and B' are their inverses; this structure isolates the effect on targeted pieces while restoring disrupted elements.[49] For example, in corner permutation, a commutator might cycle three corners with minimal disruption to the rest of the cube, leveraging the Pocket Cube's corner-only mechanics for efficient algorithm design.[49] Software tools like Cube Explorer facilitate the generation and analysis of Pocket Cube algorithms by exhaustively searching the puzzle's configuration space to produce optimal or minimal-move sequences in standard notation. Developed by Herbert Kociemba, this program outputs algorithms for specific cases, aiding in the discovery of commutators and other representations for research or custom solving methods.[50]Speedcubing and Records
Competition Formats
The World Cube Association (WCA), founded in 2003, serves as the governing body for official Pocket Cube competitions, sanctioning events at major gatherings such as World Championships and regional Nationals.[51] These competitions adhere strictly to WCA regulations to ensure fairness and consistency across global events.[52] Standard formats for the 2x2x2 Cube event include a cutoff round with a best of 2 (Bo2) phase, where competitors must record two valid solves below a designated cutoff time to qualify for the subsequent average of 5 (Ao5) round.[52] In the Ao5 round, five solves are attempted, excluding the fastest and slowest times to compute the average of the middle three; for final rounds involving eight or fewer competitors, a mean of 3 (Mo3) or best of 1 (Bo1) may be employed instead.[52] Each solve begins with a 15-second inspection period, during which the puzzle cannot be rotated, followed by a default 10-minute time limit per attempt.[52] Scrambles are produced via the official WCA software, generating random sequences of at least 10 moves (with a maximum of 25) to reach valid positions, distributed to judges for application under supervision.[53] Equipment must consist of a standard, fully assembled 2x2x2 Cube with six solid colors on its stickers and no extraneous markings, logos, or textures that could aid solving; speedcubes are permitted provided they meet these criteria and remain unmodified during the event.[52] Timing utilizes approved Stackmat electronic timers, specifically models G3, G4, or G5, operated with the standard mat and procedure to record results to the hundredth of a second.[54]Single Solve Records
The single solve records for the Pocket Cube track the fastest individual times achieved in official World Cube Association (WCA) competitions, emphasizing peak performance under timed conditions. The current world record is 0.39 seconds, set by Ziyu Ye of China during the first round of the 2x2x2 Cube event at the Hefei Open 2025 on October 25, 2025. This solve broke the previous record of 0.43 seconds held by Teodor Zajder of Poland since the Warsaw Cube Masters 2023.[55][56] Historical progression of the single solve record illustrates the evolution of speedcubing, from initial times exceeding 6 seconds to sub-0.4 seconds today. In 2009, the record stood at 6.88 seconds, with significant advancements leading to the first sub-1 second solve in 2010 by Rowe Hessler (0.96 seconds). The sub-0.5 second barrier was first crossed in 2023 by Teodor Zajder, reflecting improvements in solving efficiency.[56] Among the fastest official single solves, the top performances as of November 2025 include times all under 0.5 seconds, showcasing elite execution. Representative examples from WCA-official data are:| Rank | Competitor | Time | Competition | Date |
|---|---|---|---|---|
| 1 | Ziyu Ye (China) | 0.39 | Hefei Open 2025 | Oct 25, 2025 |
| 2 | Teodor Zajder (Poland) | 0.43 | Warsaw Cube Masters 2023 | Oct 14, 2023 |
| 3 | Max Park (USA) | 0.45 | J Perm World Cup 2023 | Aug 5, 2023 |
| 4 | Tymon Kolasiński (Poland) | 0.47 | Polish Nationals 2023 | Jun 17, 2023 |
| 5 | Guanbo Wang (China) | 0.47 | Northside Spring Saturday 2022 | Mar 26, 2022 |