Basic Cube Notation
There are 6 faces on a cube. Each face is represented by a letter, according to where it is located. These faces make the most sense when you hold the cube with one face parallel to the ground and one face facing you, but algorithm pages will often display the cube so that you can see the front, right, and top faces. The six faces are:
- F (Front) - the side facing you.
- U (Up) - the side facing upwards.
- R (Right) - the side facing to the right.
- B (Back) - the side facing away from you.
- L (Left) - the side facing to the left.
- D (Down) - the side facing downwards.
A turn of one layer of one of the six faces of the cube is written by adding a suffix to the face's name. There are three possible turns that can be applied to a face, and all moves should be applied as if you were looking at the face straight-on. Using the U face as an example, the following are possible turns:
- U - A 90-degree clockwise turn of the U face.
- U' - A 90-degree counterclockwise turn of the U face.
- U2 - A 180-degree turn (either clockwise or counterclockwise) of the U face.
Note that for U2, some people will write a clockwise 180-degree turn as U2 and a counterclockwise 180-degree turn as U2'. This is only necessary for puzzles such as the Megaminx and when describing fingertricks.
Cube rotations involve turning the entire cube. Any position can be solved without these moves, but you will often see them in algorithms. The possible cube rotations, which can also be modified with ' or 2 like a face turn, are:
- x or [r] - a rotation of the entire cube as if doing an R turn.
- y or [u] - a rotation of the entire cube as if doing a U turn.
- z or [f] - a rotation of the entire cube as if doing an F turn.
On the 3x3x3, slice turns are popular in algorithms, although they are never needed in scrambling. These moves are defined in a very inconsistent way, so watch out. The possible slice moves, which can again be modified with ' or 2, are:
- M - a move of the Middle layer (between R and L), in the same direction as an L turn.
- E - a move of the Equatorial layer (between U and D), in the same direction as a D turn.
- S - a move of the Standing layer (between F and B), in the same direction as an F turn.
On the 4x4x4 and larger puzzles, single-layer turns are not enough to fully scramble or solve the puzzle. Thus there are notations to describe turns of multiple layers on the same face. A double-layer turn, for instance, might include both the outside layer and the parallel layer touching it.
Double-layer turns are also popular in algorithms for the 3x3x3. There are two main ways to write this, using the U face as an example:
- Uw - this notation is widely used by Japanese cubers and was recently adopted by the WCA.
- u - this notation is often preferred by English-speaking cubers, and originally appeared for writing down 4x4x4 and 5x5x5 moves.
For turns of more than two layers, it is impossible to use single letters to write down turns, but a popular proposal is to use numbers to show the number of layers that are being turned. There are several ways to write these turns, using the U face as an example and 3 as an example number of layers, but the best is either 3U or 3u, because putting the number after the letter can cause confusion when there is a half turn (giving it the suffix 2).