Sudoku Solving Time Calculator
Estimating Solving Time From What's Already on the Board
A Sudoku puzzle's difficulty is driven mostly by how many cells you start with — fewer given clues means more cells to deduce, and each deduction takes longer as the puzzle gets harder. This calculator estimates total solving time from the number of empty cells and a per-cell time allowance that scales with the stated difficulty level.
The Formula
A standard Sudoku grid has 81 cells, so subtracting the given clues leaves the number of cells that must be solved. The average seconds-per-cell figure is a heuristic that increases with difficulty, reflecting that harder puzzles require more scanning and deduction per cell, not just more empty cells.
Time Allowance by Difficulty
| Difficulty | Seconds per empty cell |
|---|---|
| Easy | 15s |
| Medium | 25s |
| Hard | 40s |
| Expert | 60s |
Worked Examples
| Given clues | Difficulty | Empty cells | Estimated time |
|---|---|---|---|
| 30 | Medium | 51 | ~21m 15s |
| 22 | Expert | 59 | ~59m 0s |
This is a rule-of-thumb estimate for a standard 9x9 grid (valid for 17 to 80 given clues) — actual solving time varies widely by individual skill and solving technique.
Where This Calculation Matters
- Timed challenges — setting a realistic target time before attempting a puzzle at a stated difficulty.
- Puzzle app design — calibrating difficulty labels against expected completion time for user-facing hints.
- Comparing puzzle sources — checking whether one publisher's "hard" puzzles are genuinely harder than another's, based on given-clue count.
How to Use This Calculator
- Enter the Given Clues already filled in on the puzzle (between 17 and 80 for a standard 9x9 grid).
- Select the puzzle's stated Difficulty level.
- Select Calculate to see the estimated total solving time.
Related Calculations
For a similar time estimate on a different word-based puzzle, see the Word Search Time Calculator.