Mini Thermo takes the elegant ordering rule of Thermo Sudoku and puts it on a friendly 6x6 grid with the digits 1 to 6. A thermometer's digits must strictly increase from the round bulb to the tip — and because there are only six digits, the position bounds that experts calculate on the 9x9 grid become almost automatic here. A five-cell thermometer has just two possibilities; a six-cell one has exactly one. That is why Mini Thermo is the fastest way to learn the variant.
What is Mini Thermo Sudoku?
Mini Thermo is a 6x6 Thermometer Sudoku. You fill the grid so that every row, every column, and every 2x3 box contains the digits 1 through 6 exactly once, and every thermometer increases from bulb to tip with no repeats. The bulb is the large filled circle; the tip is the far end of the line. Each puzzle has a single logical solution.
Mini Thermo Rules
- Standard mini Sudoku rules: Every row, column, and 2x3 box must contain the digits 1–6 exactly once.
- Thermometer rule: Digits along a thermometer strictly increase from the bulb to the tip.
- No ties: Equal digits are never allowed on the same thermometer.
- Bulb low, tip high: The bulb holds the smallest digit on its thermometer, the tip the largest.
Every Thermometer Run on a 6x6 Grid
| Thermometer length | Possible digit runs (bulb → tip) |
|---|---|
| 3 cells | Any strictly increasing triple, e.g. 1-2-3, 2-4-6, 3-5-6 |
| 4 cells | Runs like 1-2-3-4, 2-3-5-6, 3-4-5-6 — the bulb is 1–3, the tip 4–6 |
| 5 cells | Only 1-2-3-4-5 or 2-3-4-5-6 |
| 6 cells | Forced: 1-2-3-4-5-6 |
Notice how quickly the options vanish. Any thermometer of four or more cells already pins the bulb and tip to a tiny range, and a length-five thermometer differs by just one digit between its two solutions. That single degree of freedom is usually resolved by one crossing row or column.
Solving Strategies
1. Attack the longest thermometer first
On a 6x6 grid a five- or six-cell thermometer is nearly solved on sight. Place its forced or near-forced run, and the digits it drops into rows, columns, and boxes cascade through the rest of the grid.
2. Pencil the position window
For each thermometer cell, mark the min and max it can hold given its index (index i is at least i+1, at most 6 minus the cells after it). Even short thermometers eliminate several candidates this way before you look at anything else.
3. Squeeze from both ends
If a bulb can't be 1 because a 1 already sits in its box, every cell above it climbs by one. Capping the tip pushes the earlier cells down. Alternating between the two ends is the core thermometer move — and on six digits it resolves fast.
4. Finish with classic scanning
Thermometer bounds narrow candidates; rows, columns, and boxes place them. Every technique from classic Mini Sudoku — cross-hatching, naked singles, pairs — applies unchanged.
Tips for Beginners
- Memorize the length-5 pair. A five-cell thermometer is always 1-2-3-4-5 or 2-3-4-5-6 — knowing this alone cracks many puzzles.
- The bulb is never 6, the tip never 1. Extremes are off-limits at the wrong end.
- Check each border of a placed digit. A new number tightens the windows of every thermometer cell it shares a row, column, or box with.
- Use candidates freely. Auto pencil marks in Sudoku - Brain Puzzles keep each thermometer's window visible.
- Step up when ready. The full 9x9 Thermo Sudoku uses the exact same logic on a wider range.
Mini Thermo is one of the best puzzle-per-minute values in the Sudoku family: a complete, self-contained ordering system you can learn in a single solve and enjoy for years. Master the runs on the small grid, and the 9x9 version becomes a natural encore.