Work out sudoku difficulty rating instantly with clear inputs, formula shown and shareable results.
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.
Scoring model
score = technique weight + 25·(81 − givens)/64 + 1.5·(9 − fewest box clues), capped at 100
17 for a puzzle with a unique solution, proved exhaustively by computer search in 2012.
No. A 22-clue puzzle solvable by simple scanning is easier than a 30-clue puzzle needing an X-wing.