What Does the Prime (') Symbol Mean in Cube Notation?

Pick up any beginner algorithm sheet and you'll quickly run into letters with a little apostrophe attached: R', U', F'. That tiny mark, called the prime symbol, is one of the most important pieces of Rubik's Cube notation to understand. Once you know what it means, the rest of the notation system falls into place surprisingly fast.

The short answer: a prime means turn that face counter-clockwise by 90 degrees. A letter alone (like R) means clockwise. That's it. But there's a bit more nuance worth knowing, especially for faces like L, D, and B, where "clockwise" depends on which direction you're looking.

At a Glance

• A prime (') after a face letter means turn that face 90 degrees counter-clockwise. No prime means clockwise.
• R2 (or any letter plus 2) means a 180-degree turn, where direction doesn't matter.
• Always judge "clockwise" from the perspective of looking straight at the face being turned, not from your normal front-of-cube view.
• L, D, and B trip people up because their "clockwise" direction is not the one you'd guess while facing the front of the cube.
• A move and its prime always cancel out: R R' returns every piece to where it started.
• Some older texts use Ri instead of an apostrophe; both mean the same counter-clockwise turn.

The Basics: Clockwise vs. Counter-Clockwise

Standard cube notation gives each face a letter based on its position relative to you when you hold the cube in a normal solving grip:

• R, Right face
• L, Left face
• U, Upper (top) face
• D, Down (bottom) face
• F, Front face (the side facing you)
• B, Back face

Every move is one quarter turn, 90 degrees, unless a 2 follows the letter. So the notation system really has just three versions of each move:

Notation	Meaning	Degrees	Direction reference
R	Turn the right face 90° clockwise	90°	As viewed from that face
R'	Turn the right face 90° counter-clockwise	90°	As viewed from that face
R2	Turn the right face 180°	180°	Direction irrelevant

The prime symbol is always written immediately after the face letter, before any space or the next move in the sequence. You'll hear it spoken aloud as "R prime," "U prime," and so on. Some older guides write it as Ri (i for inverse); the speedsolving.com wiki's notation reference documents both forms as equivalent, though the apostrophe version is by far the most common today. This is not a casual convention either: the World Cube Association's official regulations formalize face-turn notation (Article 12) for exactly this reason, so that a written algorithm means the same thing to every competitor worldwide.

How to Actually Perform a Prime Move

The trickiest part for beginners isn't understanding the concept, it's knowing which way to physically rotate your hand. The rule that makes it click:

Always imagine you are looking directly at the face you're about to turn. Clockwise from that perspective is the regular move; counter-clockwise from that perspective is the prime.

R vs. R'

Hold the cube in front of you. Now look at just the right face, the slab of stickers on the right side. When you turn it so the top goes away from you and the bottom comes toward you, that is R (clockwise as seen from the right). When you reverse that, top comes toward you, bottom goes away, that is R' (counter-clockwise as seen from the right).

Try it a few times. R followed immediately by R' puts every piece back where it started. They undo each other perfectly, which is why primes are sometimes called "inverse" moves.

U vs. U'

Now look down at the top face of the cube. Turn the top layer so the front row goes to your right, that is U (clockwise when viewed from above). Turn it the other way, front row going left, and that is U'. Again, U then U' returns you to the same position.

Why L, D, and B Catch People Off Guard

The "look at the face" rule is easy to apply for R, U, and F because those faces are in your natural line of sight. But for L, D, and B, you have to mentally flip your perspective.

• L' means counter-clockwise when viewed from the left side, which means the top of the left face comes toward you (the opposite of R).
• D' means counter-clockwise when viewed from below, which means the front row of the bottom layer goes to your left (the opposite of U').
• B' means counter-clockwise when viewed from behind the cube, which ends up looking clockwise when you're staring at the front.

This is where beginners often make mistakes and wonder why their cube is scrambling further instead of solving. A simple check: if you turn a face and the cube looks more scrambled than before rather than progressing toward your goal, stop and re-verify the direction before continuing. When in doubt, flip your mental camera to the face in question before turning.

A quick way to build the L, D, and B habit without a full algorithm: hold the cube in your normal grip and run L L' five times, watching only the left face. Then do the same with D D', watching the bottom layer from below by tilting the cube slightly. Then B B', actually rotating the whole cube in your hands so the back face is briefly in front of you. This isolates the three problem faces one at a time, instead of trying to sort them out mid-algorithm where a mistake is harder to catch.

Prime Moves in Real Algorithms

Prime moves aren't a rare curiosity, they show up constantly. The most famous beginner move sequence is the trigger used in most beginner last-layer methods:

R U R' U'

That sequence is four moves: turn the right face clockwise, turn the top clockwise, turn the right face counter-clockwise, turn the top counter-clockwise. Repeated six times in a row, it returns the cube to its exact starting state. Repeated the right number of times at the right moment in a solve, it cycles specific corner pieces without disturbing others.

Nearly every beginner-friendly algorithm for solving the last layer contains at least one prime move. Some contain four or five. Once your hands know the difference between R and R' by feel, without thinking, algorithm execution becomes much smoother.

For a closer look at how algorithms are structured and what makes them work, check out how to read a Rubik's Cube algorithm.

Building Muscle Memory for Primes

Reading prime notation is one thing; performing it reflexively under a little pressure is another. A few habits that help:

• Practice isolated pairs. Do R R' ten times in a row, watching your hand motion. Then U U'. Then L L'. Focus on the direction, not the speed.
• Say the move aloud as you do it. "R prime" while you turn helps your brain form the association.
• Use the cancellation test. If you do R' and your cube looks different from after R, you got it right. If it looks the same, you accidentally did R twice, recheck your direction.
• Slow down on L, D, and B. Until these feel natural, pause a beat before executing them and consciously ask: "Which way is counter-clockwise from the perspective of this face?"
• Time yourself on isolated drills. Ten reps of R R' in under five seconds, with no wrong turns, is a reasonable benchmark that most people hit within a week of short daily sessions.

Speed comes with repetition. A week of regular practice with the basic triggers will make prime moves feel as automatic as the plain ones.

A Note on Double Primes

You will occasionally see R2' in advanced notation. This means a 180° turn in the counter-clockwise direction, useful in some speedcubing contexts to indicate preferred turning direction, though for a 180° move it makes no practical difference in the result. Beginners can safely ignore this until much later.

For a solid foundation on all the face letters and what they refer to, the guide on Rubik's Cube notation explained covers every move type from scratch.

Why Prime Moves Matter for Solving

Beyond just reading algorithms, understanding primes helps you start to see why algorithms work. Many solving sequences are designed around the idea that R U R' does something useful to the front-right slot while the U' at the end "cancels out" the setup, leaving everything else undisturbed. This concept, setting up moves and then reversing the setup, runs through the entire solve method.

Primes also let you reverse any sequence. If R U R' U' does something, then executing those moves in reverse order and with all directions flipped, U R U' R', undoes it exactly. This is not just a solving trick, it reflects the underlying math: the set of all possible cube moves forms a mathematical group, and the Rubik's Cube group article explains how every move has a well-defined inverse, which is precisely what a prime represents. This kind of thinking becomes valuable when you advance beyond beginner methods and want to understand algorithms rather than just memorize them.

It all connects back to the fact that centers stay fixed while edges and corners orbit around them. If you're fuzzy on why that structural fact matters, why the centers never move and why it matters is worth reading alongside this one.

FAQ

What does the apostrophe mean on a Rubik's Cube move?

The apostrophe, called the prime symbol, means turn that face one quarter turn (90°) counter-clockwise, as viewed looking directly at that face. For example, U' means turn the top layer counter-clockwise when seen from above.

Is R' the same as doing R three times?

Yes. Three clockwise quarter turns total 270°, which is the same end result as one 90° counter-clockwise turn. In speedcubing, single prime moves are preferred over doing any move three times, one rotation is simply faster.

How do I know which direction is counter-clockwise for the B face?

Look at the cube from behind so the back face is now directly in front of you. Counter-clockwise from that viewpoint is B'. From the normal front-of-cube perspective, a B' move will look like a clockwise turn, which is why B moves trip people up at first.

Why do algorithms use so many prime moves?

Prime moves let algorithm designers cancel out setup moves, preserve pieces that shouldn't change, and cycle specific pieces in controlled ways. Without primes, most useful algorithms would either be much longer or impossible to write.

Can I solve a Rubik's Cube using only clockwise moves and no primes?

Technically possible for some states, but in practice no, the prime moves are essential. Avoiding them would mean replacing each prime with three clockwise turns of the same face, making algorithms three times as long and physically awkward to execute.

Does the prime symbol mean the same thing on notation for bigger cubes like the 4x4 or 5x5?

Yes. The prime always means counter-clockwise from the perspective of the layer being turned, whether that's an outer face letter like R or an inner-slice or wide-move letter like Rw or r. Bigger cubes add more letters to track, but the direction rule for primes never changes.