The 12 balls puzzle, also known as the twelve balls problem or weighing puzzle, is a classic logic puzzle where you must identify one odd ball among twelve using a balance scale in only three weighings.

Logic puzzle simulator

Find the odd ball.
Beat the scale.

Three weighings, one odd ball. Explore the classic problem with a tactile, drag-and-drop layout that adapts to desktop and touch.

Balls 12
Weighings 3
Mission Identify one

Weighing Twelve Balls on a Scale: ①②③④ ⚖ ⑤⑥⑦⑧

Here is a classic brain-teaser puzzle from 1945: You are given twelve identical-looking balls and a two-sided balance scale. One of the balls is of a different weight, although you don't know whether it is lighter or heavier. How can you use just three weighings of the scale to determine not only what the different ball is, but also whether it is lighter or heavier?

Time 0:00

Puzzle setup

Choose the odd ball or let chance decide.

  1. 01 Arrange Build both groups
  2. 02 Weigh Read the balance
  3. 03 Deduce Lock your answer
  • Desktop: click a ball to select; click-and-drag to box-select.
  • Drag the selected balls onto the left or right scale.
  • Desktop: double-click a ball to mark it excluded (green).
  • Keyboard: focus a ball, then use ←/→ to move it to a pan, ↑ to return it, and X to exclude it.
  • Click "Weigh" to compare, then repeat up to three times.
  • Use "Undo" to revert the last weighing or "Clear scale" to reset placements.
  • When ready, enter your guess in the solution form.
Ball pool
Scale
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Weigh history
What is the different ball?
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