What is the minimum number of clues a valid Sudoku needs?

The mathematical minimum for a uniquely-solvable 9x9 Sudoku is 17 clues. Any fewer and the puzzle has more than one solution, which violates the Sudoku standard.

How does clue count relate to difficulty?

More pre-filled clues leave fewer empty cells, making deduction easier. Puzzles with 36 or more clues are typically Easy; 28–35 are Medium; 22–27 are Hard; 17–21 are Expert. These thresholds follow widely-used publishing conventions.

Can two puzzles with the same clue count have different difficulty?

Yes. Clue count is a primary but not exclusive factor. The position of the clues and the solving techniques required also affect perceived difficulty. This tool gives a reliable first approximation based on count alone.

Why does my puzzle app show a different rating?

Commercial apps often use solver algorithms that test which logical techniques are needed (e.g., X-wing, swordfish) in addition to clue count. Our tool uses clue count — the most accessible and universally understood metric.

What if I enter a value outside 17–81?

The tool flags the input as invalid. A Sudoku with fewer than 17 clues cannot be uniquely solved, and 81 clues means a fully-filled grid with no blanks — neither is a real puzzle.

Sudoku Difficulty Rater

Name: Sudoku Difficulty Rater
Availability: InStock
Author: Nham Vu

Enter the number of given clues in your Sudoku puzzle to instantly find out if it is Easy, Medium, Hard, or Expert difficulty.

Count Your Clues

Count all pre-filled numbers in the 9x9 grid and enter the total below.

Visual: cells light up as you increase the clue count.

Number of given clues

Quick set:

Difficulty Rating

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Difficulty Scale

Easy

36–58 clues

Medium

28–35 clues

Hard

22–27 clues

Expert

17–21 clues

Note: 59–81 clues is a near-complete or fully-filled grid — not a standard puzzle.

Summary