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Sudoku Difficulty Rating Calculator

Work out sudoku difficulty rating instantly with clear inputs, formula shown and shareable results.

About Sudoku Difficulty Rating Calculator

Sudoku difficulty depends far more on which solving techniques are required than on the number of givens. This model weights the hardest necessary technique most heavily, then adds smaller penalties for few clues and for sparse boxes.

Formula

Scoring model

score = technique weight + 25·(81 − givens)/64 + 1.5·(9 − fewest box clues), capped at 100

Worked example

With the default values below, Sudoku Difficulty Rating Calculator returns Difficulty score out of 100 of 63.48. Change any input above and every figure here is recalculated in your browser.

Inputs used

Number of given digitsaccepts 17–81
26
Hardest technique neededone of Single candidate only, Hidden singles, Box-line reduction, X-wing or swordfish, Trial and error required
Box-line reduction
Fewest givens in any 3×3 boxaccepts 0–9
1

Results

Difficulty score out of 100
63.48
Difficulty band
Hard
Empty cells to fill
55
Weight of the hardest technique
30

Step by step

  1. 1Values used
  2. 2Scoring model
  3. 3Difficulty score out of 100= 63.48
  4. 4Difficulty band= Hard
  5. 5Empty cells to fill= 55
  6. 6Weight of the hardest technique= 30

Assumptions and limits

  • The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

What is the minimum number of givens?

17 for a puzzle with a unique solution, proved exhaustively by computer search in 2012.

Do fewer clues always mean harder?

No. A 22-clue puzzle solvable by simple scanning is easier than a 30-clue puzzle needing an X-wing.

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