🎚️ Comprehensive Guide

Sudoku Difficulty Levels — The Complete Guide

Open any sudoku app, puzzle book or newspaper and you'll see the same little label: easy, medium, hard or expert. But what do those words actually mean? Why does one 'easy' puzzle finish in five minutes while another 'easy' grid stops you cold? And how do you know when you're ready to step up?

This is the most thorough guide to sudoku difficulty levels you'll find anywhere. We explain every level in plain English, share the clue counts and solve times you can expect, list the techniques each level needs, and show how difficulty changes across grid sizes (4×4, 6×6, 9×9, 16×16) and variants like killer, jigsaw and X-sudoku. Whether you're a brand-new puzzler, a parent picking the right book for your child, or a curious solver who wants to know how the rating actually works, you're in the right place.

We've designed this guide so you can read it top-to-bottom or jump straight to the section you need. The table of contents below links to every part. Bookmark the page and come back whenever you're choosing your next puzzle.

What's in this guide

The four sudoku difficulty levels at a glance

Almost every sudoku site uses the same four-level scale: easy, medium, hard and expert (sometimes called "evil" or "extreme"). Here is a quick comparison so you can pick the right level for the time and skill you have.

Level Clues given Solve time Best for
Easy 36–45 clues 5–15 min Beginners, kids, daily warm-ups
Medium 30–35 clues 10–25 min Confident beginners and casual solvers
Hard 26–30 clues 20–45 min Solvers who use pencil marks fluently
Expert / Evil 22–26 clues 40–90 min Experienced solvers who love a challenge

Every level explained in detail

Below is a deep dive into each level — the techniques you need, the time it takes, who it's for, and how it actually feels to play. The clue counts and times are typical ranges; every puzzle is a little different.

Easy

The friendly starting point

Clues given
Around 36 to 45 starting clues out of 81 cells.
Solve time
5 to 15 minutes for most solvers, faster with practice.
Best for
Brand-new puzzlers, kids learning the rules, and anyone who wants a quick, satisfying win — perfect with a morning coffee or as a bedtime wind-down.
Techniques you need
Scanning, cross-hatching, last-digit moves, naked singles and the occasional hidden single. No pencil marks needed; you can usually solve every cell by simply looking at the grid.
How it feels to play
Easy puzzles flow. You almost always have a next move in plain sight, and one number leads to another like dominoes. There are very few 'stuck' moments — and when you finish, the puzzle is one solid, satisfying chain of logic.

💡 Pro tip: Use easy puzzles to build habits, not to race. Practise scanning every digit 1 through 9 in order, even when you spot an obvious answer first. Good habits at this level make every harder level much easier.

Medium

Where strategy starts to matter

Clues given
Around 30 to 35 starting clues.
Solve time
10 to 25 minutes once your scanning is reliable.
Best for
Confident solvers who can finish an easy puzzle without getting stuck, and kids who've outgrown 4×4 and 6×6 grids.
Techniques you need
Everything from easy, plus consistent use of hidden singles. You may also want a few light pencil marks in the trickier corners — but they are still optional on most medium puzzles.
How it feels to play
Medium puzzles have one or two moments where the obvious move stops appearing. Instead of giving up, you slow down, scan one digit at a time, and a hidden single quietly opens the next door. You'll feel yourself thinking — but not struggling.

💡 Pro tip: When you feel stuck, switch to digit-by-digit scanning. Pick a number 1 to 9 and ask "where does it go in this row?" then "this column?" then "this box?" That single habit unlocks almost every medium puzzle.

Hard

Pencil marks become your best friend

Clues given
Around 26 to 30 starting clues.
Solve time
20 to 45 minutes — and a long pause or two is normal.
Best for
Solvers who already use pencil marks comfortably and want a real workout, plus older kids and teens who have mastered medium puzzles.
Techniques you need
Naked pairs, hidden pairs, pointing pairs and box-line reduction. You will almost certainly need pencil marks across most empty cells. Many hard puzzles require a naked or hidden triple too.
How it feels to play
Hard puzzles bite back. The opening few cells fall quickly, then everything stalls. Suddenly you spot a naked pair, and the puzzle starts moving again. There's a real sense of detective work — every clue you eliminate is a small victory.

💡 Pro tip: Pencil-mark every empty cell early — don't wait until you're stuck. Notes don't slow you down; they speed up everything that comes next. And if you reach a wall, take a five-minute break. Hard puzzles are kinder to fresh eyes.

Expert (Evil / Extreme)

Logic at its purest and most demanding

Clues given
Around 22 to 26 starting clues — close to the theoretical minimum of 17.
Solve time
40 to 90 minutes for most solvers; longer is fine.
Best for
Experienced sudoku fans who want a real puzzle to think about across a whole afternoon — not usually recommended for beginners or younger children.
Techniques you need
Everything from hard plus advanced patterns: X-Wing, Y-Wing (XY-Wing), Swordfish, XYZ-Wing, colouring chains and sometimes Unique Rectangle. Full pencil marks are essentially required throughout.
How it feels to play
Expert puzzles are slow, beautiful and deeply satisfying. You will sit and stare. You will think you've made a mistake. Then a single small deduction — a wing or a chain — quietly resolves a candidate, and a cascade of moves opens up. Finishing one feels like climbing a mountain.

💡 Pro tip: Treat each expert puzzle as a project, not a sprint. Scribble notes, leave the puzzle on the table, come back fresh. And remember: if you ever feel forced to guess, you've missed something — every real expert sudoku has one solution reachable by logic alone.

How sudoku difficulty is actually determined

A sudoku puzzle's level is not just about how many clues are missing. Modern sudoku solvers (the kind that rate puzzles for apps and books) look at several factors. Here are the most important ones.

  • The number of starting clues

    Easy puzzles tend to start with 36–45 clues, expert puzzles closer to 22. Fewer clues usually means harder, but only roughly — the position of those clues matters far more than the count.

  • How the clues are placed

    Two puzzles with the same number of clues can have wildly different difficulty. Clues spread evenly across boxes are friendlier; clues clumped in one corner force the solver to deduce the rest from far away.

  • The hardest required technique

    Every puzzle has a "ceiling" — the most advanced technique you must use to solve it logically. A puzzle that needs only naked singles is easy; one that needs an X-Wing is hard; one that needs a Swordfish is expert.

  • How often hard moves are needed

    A puzzle that requires one X-Wing once is easier than a puzzle that requires three of them. Difficulty raters count the number of advanced moves, not just the type.

  • How easy the moves are to see

    Some moves are technically simple but visually hidden. Two puzzles can both require only naked singles, yet one might bury those singles inside cells with seven candidates each. That visual load adds difficulty.

  • Uniqueness and consistency

    A real sudoku puzzle has exactly one solution and never requires guessing — every step can be reached by logic. Difficulty raters reject puzzles that need trial-and-error.

How difficulty changes with grid size

The classic sudoku grid is 9×9, but kids and curious solvers often start with smaller grids. Here's how the difficulty scale shifts when the grid changes size — and which size to pick for which player.

  • 4×4 sudoku

    Very easy

    A mini sudoku using only digits 1–4. Even an "expert" 4×4 is easier than an easy 9×9 — perfect first puzzle for ages 4 and up. Most 4×4 puzzles solve with scanning alone.

  • 6×6 sudoku

    Easy to medium

    Uses digits 1–6 with 2×3 boxes. A friendly stepping stone for ages 6+. Expert 6×6 puzzles teach hidden singles and naked pairs without overwhelming a young solver.

  • 9×9 sudoku

    The full scale (easy → expert)

    The classic grid. The four-level easy/medium/hard/expert scale was designed for this size. When sudoku is rated without specifying a size, it almost always means 9×9.

  • 16×16 sudoku

    Significantly harder

    Uses 1–9 plus letters A–G in 4×4 boxes. Even an 'easy' 16×16 sudoku takes most solvers as long as a hard 9×9. A great next step once expert 9×9 puzzles feel routine.

How difficulty changes across sudoku variants

Sudoku variants change the rules — and that changes the difficulty too. A 'medium' killer sudoku is usually harder than a medium classic puzzle. Here's how the popular variants compare to a regular 9×9, so you can choose the right next puzzle.

Killer Sudoku

About one level harder than classic.

Why: You still need every classic sudoku rule, plus mental arithmetic for the cage sums. A medium killer is closer to a hard classic 9×9.

Play killer sudoku

Jigsaw Sudoku

About the same level — sometimes a touch harder.

Why: The wiggly regions break your usual visual habits. The same techniques work, but spotting them takes longer until your eyes adjust.

Play jigsaw sudoku

X-Sudoku

About the same as classic, with extra easy wins early.

Why: The two diagonals act as bonus clues. Easy puzzles feel easier; expert puzzles feel just as hard.

Play X-sudoku

Color Sudoku

Easier than classic at every level.

Why: Same rules, but colours are easier to scan than digits. A brilliant first sudoku for kids who cannot read numbers yet.

Play color sudoku

Battleship Sudoku

A bit harder than classic.

Why: You play sudoku and a battleship deduction puzzle at once. Two layers of logic make the same level feel like more work.

Play battleship sudoku

Circle Sudoku

About the same — but visually disorienting at first.

Why: The same logic works, but a round grid hides familiar shapes. Allow extra time on your first few rounds.

Play circle sudoku

How to level up step by step

Want to climb the difficulty ladder confidently? This is the practice plan we recommend — try one step every week or two, and resist the urge to skip ahead. The technique you skip is the technique that stops you later.

  1. Step 1 — Master easy 9×9

    Solve at least ten easy puzzles in a row without getting stuck. You should feel like there's always an obvious next move. If you do, your scanning is solid and you're ready to step up.

  2. Step 2 — Add hidden singles

    Practise spotting hidden singles on easy and medium puzzles. Every time you place a digit, ask where else it could go in nearby boxes. This is the bridge from easy to medium.

  3. Step 3 — Learn pencil marks

    Switch on pencil marks on a medium puzzle. Mark every empty cell. The first time it feels slow — by the third puzzle it'll feel natural. Pencil marks are the gateway from medium to hard.

  4. Step 4 — Naked and hidden pairs

    On hard puzzles, look for two cells in the same row, column or box that share exactly the same two candidates. Erase those digits from every other cell in the unit. You've just unlocked the most useful pattern in sudoku.

  5. Step 5 — Pointing pairs and box-line reduction

    When all candidates for a digit inside one box sit in the same row or column, the digit must live there. This single trick unlocks most hard puzzles and many expert ones.

  6. Step 6 — X-Wing, Y-Wing and beyond

    These advanced patterns are the bridge to expert. Take one technique a week. Don't worry about chaining them yet — practise spotting one at a time on real puzzles.

Common myths about sudoku difficulty

Once you start paying attention to difficulty, you start hearing a lot of confident-but-wrong claims. Here are the ones we see most often — and the truth behind them.

"More empty cells always means harder."

Not really. Two puzzles with the same number of clues can rate completely different levels. The placement of the clues — and the techniques required — matter more than the raw count.

"Easy puzzles are for beginners only."

Many strong solvers do an easy puzzle every day as a warm-up. Easy puzzles are also the best way to practise good scanning habits, which feed every harder level.

"Expert puzzles need guessing."

A genuine sudoku puzzle — at any difficulty level — has exactly one solution that can be reached by logic alone. If you feel forced to guess, you missed a step. Slow down, switch on pencil marks and look again.

"You should solve hard puzzles fast."

Even strong solvers take 20–45 minutes on a hard puzzle. Speed is a side effect of practice, not the goal. Better to finish a hard puzzle in 40 minutes than a medium one in 10.

"All sudoku apps rate puzzles the same way."

Definitely not. One app's 'easy' might be another's 'medium'. If you're new to a site, start a level below where you usually play and adjust from there.

"Kids should start at easy 9×9."

For most kids, 4×4 and 6×6 grids are a much friendlier first step. They use the same logic, finish in a few minutes, and build confidence quickly. Easy 9×9 is a great next step once 6×6 feels comfortable.

Frequently asked questions about sudoku difficulty

What are the four sudoku difficulty levels?

Almost every sudoku site uses the same four-level scale: easy, medium, hard and expert (sometimes called evil or extreme). Each level reflects a typical clue count and the hardest technique required to finish the puzzle by logic alone — no guessing.

How many clues are in an easy sudoku?

An easy 9×9 sudoku usually starts with around 36 to 45 clues out of 81 cells. The puzzle can be solved with scanning, last digits, naked singles and a few hidden singles — no pencil marks required.

What is the hardest sudoku difficulty?

The hardest standard tier is "expert" (also called evil or extreme). Expert puzzles tend to start with 22–26 clues and require advanced patterns like X-Wing, Y-Wing or Swordfish. There are also community-rated puzzles labelled "diabolical" or "fiendish" that go even further, but those are not part of the standard four-level scale.

How long should an easy sudoku take?

Most solvers finish an easy 9×9 sudoku in 5 to 15 minutes. Beginners can take longer, and that is completely fine. With practice, the time naturally drops to under 10 minutes — but the goal is enjoying the puzzle, not racing it.

Why does my "easy" puzzle feel hard?

Two reasons. First, sudoku ratings vary between apps — one site's "easy" can be another's "medium". Second, even within one rating, individual puzzles vary. If a puzzle frustrates you, switch on pencil marks, scan each digit one at a time, or simply try a different easy puzzle. Both habits help.

What is the minimum number of clues a sudoku can have?

Mathematicians have proved that 17 clues is the minimum for a 9×9 sudoku puzzle to have a unique solution. Almost no commercial puzzles ship at that count — most expert puzzles start at around 22–26 clues, which already requires advanced techniques.

How is sudoku difficulty rated?

A sudoku solver examines the puzzle and works out the most advanced technique required to solve it without guessing. Combined with how often hard moves are needed and how many clues are present, that gives a rating. The exact formula varies between apps, but the order — easy, medium, hard, expert — is universal.

Are children able to do hard sudoku?

Yes — but usually only after they have grown comfortable with easy and medium puzzles, and learned how to use pencil marks. A motivated 10- or 11-year-old who plays regularly can absolutely tackle hard puzzles. For younger children, 4×4 and 6×6 grids are a much friendlier route.

Is medium sudoku harder than killer sudoku?

Roughly speaking, a medium killer sudoku feels about as hard as a hard classic 9×9, because killer adds mental arithmetic on top of every classic deduction. If you are comfortable on hard classic puzzles, medium killer is a good next step.

Should I always finish a hard puzzle before trying expert?

Not necessarily — but you should be able to finish a hard puzzle without guessing. Expert puzzles introduce advanced patterns (X-Wing, Y-Wing, Swordfish) that build directly on the pairs and pointing pairs you learn at hard. Skipping ahead too soon is the most common reason expert puzzles feel impossible.

Why are some "expert" puzzles unsolvable for me?

Almost certainly because one or more of the advanced techniques the puzzle requires is not yet in your toolkit. Identify the technique by checking a hint, learn that one technique on easier puzzles first, then come back. There is no shame in this — every expert solver did exactly the same thing.

Are there sudoku levels harder than expert?

Yes, but they are unofficial. Sites sometimes use labels like "diabolical", "fiendish", "master" or "extreme" for puzzles that need very long deduction chains, multiple X-Wings, or rare patterns like Sue de Coq. They are wonderful brain workouts, but the four-level easy/medium/hard/expert scale is by far the most widely used standard.

Pick your level and play!

That's everything you need to know about sudoku difficulty levels — every tier explained, every factor that goes into the rating, and a clear path from beginner to expert. The single best thing you can do now is play. Pick a level one notch below your comfort zone for a warm-up, or one notch above to stretch yourself. Whichever you choose, take your time and enjoy that quiet click when the answer falls into place.

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