Sitting down with your first sudoku and staring at all those empty cells, it's easy to feel stuck before you've even started. Where do you even start? Should you just guess? Most people either give up at this point or start filling in numbers at random — and neither approach gets you anywhere.

Sudoku runs on systematic elimination — not gut feeling. Learn to read the grid in the right sequence, and the rest follows on its own. This guide takes you from the basic rules all the way through your first real techniques — with common mistakes and a practical action plan included.

What Is Sudoku?

Fill a 9×9 grid with the numbers 1 through 9 — that's the whole game. The hard part is knowing which number belongs where.

The game traces its roots back to the 18th century and Swiss mathematician Euler's Latin squares. It took the form we know today in Japan in the 1980s, then crossed into the West in the early 2000s and swept the globe within a few years. Today, over 100 million people solve sudoku every day — because it requires neither math skills nor knowledge of any particular language. Just logic.

📌 Important Note Every valid sudoku puzzle has one and only one correct solution. If you think you've found more than one, or suspect you have, there's almost certainly a mistake somewhere.

The Basic Rules

Complex as it may look, sudoku has just three rules:

  • 📏Rows: Every digit from 1 to 9 must appear exactly once in each row.
  • 📐Columns: The same rule applies to every column.
  • 🔲3×3 Boxes: Each of the nine equal sections the grid is divided into must also contain every digit exactly once.

The puzzle gives you some cells already filled in — these are called given numbers or clues. Your job is to fill in the rest without breaking any of the rules.

💡 Why Does Difficulty Vary? Easy puzzles provide 30–36 given numbers; elimination alone is enough to solve most cells. At medium difficulty, that number drops to 25–29 and things get a bit more technical. Hard puzzles offer only 20–24 givens, and without advanced techniques like X-Wing and Swordfish, progress gets tough.
1

Survey the Grid as a Whole

Before writing a single digit, spend 10–15 seconds scanning the grid. Which row or column has the most numbers already filled in? Which areas are most constrained in terms of empty cells?

This habit looks minor. It isn't. Every experienced player does it with every new puzzle — one full look before touching anything. Denser areas give you quick wins, and those early wins build real momentum.

Pay special attention to this: if only one empty cell remains in a row, column, or box, you already know exactly which number belongs there. Fill it in and move on.

2

Apply the Elimination Method

Elimination is sudoku's core technique. The logic: figure out which numbers can't go in a cell. Whatever's left is the answer.

Pick an empty cell and ask yourself these three questions:

  • Which numbers are already in this cell's row?
  • Which numbers are already in the same column?
  • Which numbers are already in this cell's 3×3 box?

Any number that appears across those three lists is ruled out. If only one number remains — fill in the cell.

🔍 Concrete Example If a cell's row already contains 1, 2, 4, 5, 6, 7, 8, and 9, then only 3 can go in that cell. No math required — just spot what's missing.
3

Find the Singles

Naked Single

When elimination leaves only one possible number for a cell, that's called a naked single. These are the easiest spots in any sudoku — whenever you spot one, fill it in immediately and keep scanning.

Hidden Single

This one's a bit more subtle. If a particular number can only fit into one cell within a given row, column, or box, then that cell must hold that number — even if the cell appears to have other candidates.

For example, if the digit 7 could theoretically go into five different cells in a 3×3 box, but four of those are eliminated by other constraints and only one remains — that cell is 7. You won't find this by intuition; you find it by systematically checking each number one at a time.

💡 Tip Hidden singles are enough to crack most medium-difficulty puzzles. Once you get the hang of this technique, Medium puzzles start to look very different — wherever you get stuck, a systematic scan will often open things back up.

Candidate Notes: When and How to Use Them

Sometimes more than one number could plausibly go in a cell and you're not sure which one to write. That's when candidate notes come in: you jot down all the possible numbers as small marks in the corner of the cell.

Beginners often see this as unnecessary; experienced players see it as essential. Why? Because in sudoku, every number you write affects dozens of surrounding cells. Trying to keep track of everything in your head dramatically raises your error rate.

In practice: start by scanning what's already on the board and eliminating from there. Then, for the cells you still can't resolve, build a candidate list. Each time you fill in a number elsewhere, remove that number from the candidate lists of neighboring cells. When a list narrows down to a single entry — that cell is solved.

Our guide on using candidate notes correctly covers the technique in much greater depth. On Sudokum.net, press the N key to switch into note mode.

5 Mistakes Beginners Always Make

  • 1
    Starting with guesswork

    If you feel like you need to guess in sudoku, there's almost certainly a technique you haven't tried yet. Don't resort to guessing before you've fully exhausted elimination and single-number scanning.

  • 2
    Getting stuck in the same region

    If a particular 3×3 box has you stumped, look away from it. Making progress in a different row or column often feeds new information back into the area where you were stuck.

  • 3
    Skipping notes

    Everyone who says "I'll keep it in my head" hits the same wall — usually by the second Medium puzzle. Taking notes doesn't slow you down — it actually saves you from asking the same question over and over again.

  • 4
    Not checking after each entry

    Every time you fill in a number, take a quick look at that row, column, and box. Errors become layered problems the further you get into the puzzle — catching them early is much easier.

  • 5
    Forgetting to revisit as you progress

    Cells that seemed unsolvable earlier can suddenly become solvable once you've placed a new number. Scan the whole grid every now and then — solutions often open up in unexpected places.

Game Coach: What to Do When You're Stuck

If you're playing on Sudokum.net, try the Game Coach feature instead of jumping straight to a hint. It has three modes:

Mode 1

Silent

No interference at all. For those who want to work through it entirely on their own.

Mode 2

Balanced

Offers a gentle nudge when you get stuck, without giving away the answer. You keep learning.

Mode 3

Teaching

Explains which technique to use and why. It makes a real difference for beginners.

In our Daily Sudoku content, we also cover how to get the most out of Game Coach at different difficulty levels.

A Practical Plan for Solving Your First Puzzle

From theory to practice: work through these steps in order.

  • Survey the grid. Find the row or column with the highest number of filled cells.

  • Fill in the forced cells. Use row–column–box elimination to collect all the naked singles.

  • Scan for hidden singles. Check each 3×3 box to see which numbers can only fit in one cell.

  • Open candidate notes. For anything you still can't resolve, press N and note down the possibilities.

  • Repeat with new information. Every number you place feeds information into neighboring cells. Keep the cycle going from steps 1–4.

These five steps are enough to solve most Easy puzzles and many Medium ones. For more advanced techniques, check out our sudoku strategy guide.

Next Steps

If Easy puzzles no longer challenge you, it's time to move up to Medium. That's where techniques like naked pairs and hidden pairs come into play — one step beyond basic elimination.

We have a dedicated guide covering advanced sudoku techniques with thorough examples. Methods like X-Wing and Swordfish look complex at first glance, but once the logic clicks, they're surprisingly mechanical.

If you want to put yourself to the test, our Daily Sudoku system publishes a new puzzle every day. Everyone around the world solves the same puzzle on the same day, which gives you a real benchmark to measure your progress against. If you're thinking about competitive play, take a look at our competitive mode as well.

Frequently Asked Questions

  • No. Any well-formed sudoku puzzle can always be solved through pure logic. If you feel the need to guess, it means there's a technique you haven't spotted yet. Go back to elimination and single-number scanning.
  • A few hours of practice is usually enough to solve Easy puzzles properly. Medium difficulty may take a few days. Advanced techniques can take weeks — but it all depends on how much you play and how much you think things through.
  • You may not need them for Easy puzzles. For Medium and Hard, they're almost essential. Trying to keep track of everything mentally increases your error rate significantly.
  • Various studies suggest that regularly working through logic puzzles may support cognitive flexibility and concentration. It wouldn't be accurate to make definitive medical claims, but habits like sudoku do contribute to keeping the mind active.
Final Word Getting stuck on your first puzzle is completely normal. You might get stuck on your second one too. But every time you get stuck, it simply means there's something you haven't seen yet — and the moment you do see it, that same spot won't slow you down in the next puzzle. Open an Easy puzzle today. Set Game Coach to Teaching mode. Work through the steps in this guide, one by one.

If you're curious about sudoku's effects on brain health, we've dedicated a separate article to that topic.