Play Sudoku Medium Free Online: Best Sites & Strategies

You can play medium Sudoku free online at several quality sites — including 247 Sudoku, Sudoku.com, MySudokuWorld, Sudoku Royal, and 1sudoku.com. All of them offer unlimited medium-difficulty logic puzzles — the sweet spot of the number puzzle for regular solvers — with helpful features like notes, hints, and timers, and none requires a sign-up or payment to play.

What Makes Sudoku "Medium"?

The rules of this number-placement puzzle never change: fill a 9×9 grid so that every row, column, and 3×3 box contains the digits 1 through 9 exactly once (Sudoku rules). What changes with difficulty is how many starting clues (called givens) you get.

A medium puzzle starts with roughly 27 to 35 pre-filled numbers, compared with 36 to 45 on easy puzzles (MySudokuWorld). With fewer clues, naked singles — cells where only one digit is legal — dry up quickly, and you have to compare two or three units at once to find the next move.

Medium difficulty is where real solving begins. Easy puzzles can be finished with naked singles alone, but medium introduces hidden singles (a digit that can only fit one cell in a row, column, or box) and candidate notation — writing small pencil-mark notes of every possible digit for the empty cells. Importantly, you still never need to guess or learn advanced patterns like X-Wings; those arrive at hard and expert levels (MySudokuWorld). Once medium feels easy, Killer Sudoku is a popular next challenge.

A comfortable medium solve takes around 10 to 20 minutes (MySudokuWorld) — long enough to engage your brain, short enough for a coffee break.

Where to Play Medium Sudoku Online Free

Every site below was checked directly. All offer free medium-difficulty Sudoku in the browser, and none locks the medium level behind a paywall.

1. 247 Sudoku (247sudoku.com)

You hit "Play", pick Medium from four difficulty levels (Easy, Medium, Hard, Expert), and you're in a randomly generated puzzle — no account needed. It includes a timer, pencil-mode notes, number highlighting (click any digit to see all its positions, which makes hidden singles easier to spot), and a Daily Challenge with a leaderboard.

2. Sudoku.com

Sudoku.com's free medium page offers six difficulty levels (Easy through Extreme). Its interface provides notes for recording candidates, verifying entered data, and changing or removing entries, plus on-site tips for when a medium puzzle stalls — a solid all-round choice if you want harder levels later.

3. MySudokuWorld (mysudokuworld.com)

New puzzles load in one click with no account required; notes auto-update as you place digits, and you get unlimited undo, full keyboard navigation, and automatic local saving. A free account is optional, adding only XP and rank tracking — the puzzles are fully free.

4. Sudoku Royal (sudoku-royal.com)

Sudoku Royal's medium page promises free play with no downloads, no registration, and no ads. Boards typically start with around 28 to 32 filled cells, and its guide recommends the same techniques covered here: naked pairs, hidden singles, crosshatching, and scanning. A good pick for the simplest experience.

5. 1sudoku.com

The long-running 1sudoku.com offers free medium puzzles on mobile, tablet, or computer, with five difficulty levels (easy, medium, hard, expert, evil). Its standout feature is flexible error checking — flag conflicts, auto-correct, or stay silent — plus a candidates display and a show/hide solution option for when you're truly stuck.

Free Medium Sudoku Sites Compared

(Only features confirmed on each site are listed; a dash means the feature was not verified there.)

How to Play Medium Sudoku: Core Techniques

You only need four techniques to solve any medium puzzle without guessing.

1. Naked singles

Look at an empty cell and list every digit already present in its row, column, and 3×3 box. If eight of the nine digits appear, the missing one is the only legal answer. Clear all naked singles first — every placement simplifies the board.

2. Hidden singles

The single most important medium-level skill. A hidden single is a digit that looks like it could fit several cells in a unit, but when you check the crossing rows and columns, only one cell can legally take it. Scan one digit at a time across all nine boxes — your eyes will start finding them automatically.

3. Candidate notation (notes)

When singles dry up, switch on notes. Write every legal digit into each empty cell as a small pencil mark. As you confirm placements, your notes shrink — cells that narrow to a single candidate are your next moves. On medium boards you rarely need anything beyond basic notation.

4. Naked pairs

Sometimes two cells in the same row, column, or box share exactly the same two candidates — say, both show only 3 and 8. Since one of those cells must be 3 and the other must be 8, you can safely delete 3 and 8 from every other cell in that unit. This cleanup often reveals hidden singles that were buried in busy candidate lists.

Medium Sudoku Strategies and Tips

• Scan the most-filled units first. Rows, columns, or boxes with the most starting clues leave the fewest possibilities and give you the easiest early placements.
• Highlight numbers. Sites like 247 Sudoku let you click a digit to highlight all its positions — an instant view of where that number can and cannot go next.
• Never guess; use elimination. If a move isn't certain, it isn't ready. Ruling out where a digit can't go is just as productive as finding where it can.
• Hunt hidden singles digit by digit. Pick a number, sweep the whole grid for it, then move to the next number. This systematic pass finds moves that random scanning misses.
• Use notes early, not late. Open pencil marks after clearing the obvious singles — before you feel stuck. A tidy board keeps errors rare.
• Re-scan after every placement. Each confirmed digit unlocks new singles, so cycle back through the techniques after every move instead of moving on too fast.
• Work on one number at a time. Finishing all the 5s, for example, removes one whole digit of clutter and often exposes the next breakthrough.

Common Mistakes to Avoid

• Checking only one constraint. Placing a digit after checking just the row — without verifying the column and 3×3 box — is the most common source of errors. Always check all three.
• Ignoring the boxes. Rows and columns get the attention, but many hidden singles only reveal themselves inside a 3×3 box.
• Delaying notes. Waiting until the puzzle feels impossible before turning on pencil marks creates a messy board and wasted time.
• Treating candidates as guesses. Notes are logical possibilities, not guesses — each one can be removed with certainty the moment its digit appears in the same row, column, or box.
• Giving up on a technique too soon. If hidden singles stall, switch to naked pairs; if those fail, try scanning a different digit. Medium puzzles always have a logical next step.
• Rushing the opening scan. The first two minutes set up the whole solve. A thorough initial sweep saves far more time than speed-placing half-checked digits.