Play Thermometer Sudoku Online Free

Play Thermometer Sudoku online for free. Digits along each thermometer must increase from bulb to tip. Classic Sudoku rules apply.

▶ Play Thermometer Sudoku — Free
🟢 Easy 🟡 Medium 🟠 Hard 🔴 Expert

How to Play Thermometer Sudoku

  1. Standard Sudoku rules: every row, column, and 3×3 box contains 1-9.
  2. Thermometers show paths where digits must strictly increase.
  3. The bulb (round end) has the smallest digit, the tip has the largest.
  4. A 4-cell thermometer means 4 strictly increasing digits from that range.
💡 Pro Tip
A thermometer of length N forces the bulb ≤ 10−N and the tip ≥ N. Use this to narrow candidates quickly.

Frequently Asked Questions

How do thermometers work in Sudoku?

Each thermometer is a path of cells. Digits must strictly increase from the bulb (round end) to the tip. Combined with standard Sudoku rules, this creates powerful deductions.

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▶ Play Thermometer Sudoku