How do you play Hourglass Swap?

Each level gives you 2-4 hourglasses with different sand capacities. All start full on top and sand flows down at 1 unit per second. Tap any hourglass to flip it. Your goal is to reach a moment when some hourglass has exactly the target amount of sand in it (top or bottom).

What is the math behind hourglass puzzles?

Hourglass puzzles are based on the same mathematics as the classic water jug problem (Bezout identity). With hourglasses of capacity a and b, you can measure any multiple of gcd(a,b). The puzzle generates levels where the target is always achievable.

How many levels does Hourglass Swap have?

30 levels across 6 difficulty tiers. Tier 1-2 uses 2 hourglasses, Tier 3-4 uses 3, and Tier 5-6 uses 4. Each level is mathematically verified solvable via BFS.

Is Hourglass Swap free?

Yes, completely free with no download or signup. Play instantly in your browser on desktop or mobile.

Hourglass Swap

Flip sand timers. Measure exact time. Master the flow.

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How to Play

Goal: Each level gives you 2-4 hourglasses and a target time. You need to reach a moment when any hourglass has exactly the target amount of sand (top or bottom).

Sand Flow: All hourglasses start with sand on top, flowing down at 1 unit per second. The numbers on each glass show the current sand amount in top/bottom.

Flip: Tap any hourglass to instantly flip it. Top becomes bottom and vice versa.

Win: When any glass hits the exact target, you win! Fewer flips = more stars.

Reset: Tap Reset to restart the current level.

Hourglass Swap

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