Compare, resize, reveal

  1. Read the green reference. Its label states the known size and dimension.
  2. Resize the coral target. Use the slider, − / + controls or drag sideways on the board. The slider’s arrow keys make small adjustments. Enter submits a focused slider.
  3. Lock in your guess. A teal outline shows the true size. Read the measurement note and your round score, then continue.

The view fits both objects automatically while preserving one shared scale. The reference’s recorded measurement does not change as you resize the target.

Choose your mode

  • Daily: five mixed-category rounds, the same for everyone on the same UTC date. Resets at 00:00 UTC.
  • Unlimited: fresh five-round sets without a daily cap.
  • Survival: 20 seconds per round, three lives. A score below 60 or a timeout costs a life. The reveal pauses between rounds. The set ends at zero lives or after 100 rounds.
  • Category practice: unlimited sets drawn from one chosen collection.
  • Friend challenge: share a link for the same five comparisons.

Score up to 500

Every normal round has equal weight and awards up to 100 points. Half and double are equivalent proportional errors and both earn 50 points. An error factor of 1.03 or less scores 100; a factor of four or more scores zero. Read the full scoring explanation.

Build a daily streak

Complete all five mixed daily rounds on consecutive UTC dates. Your result and streak are saved in this browser. Category practice and friend challenges do not extend the daily streak. Clearing browser data or switching devices starts a separate history.

Read the source convention

The game uses a specific measurement, which may be an adult maximum, a museum estimate, a standard size or a named model. The object library gives the selected value and source. SizeGuess is a game, not a scientific assessment of your eyesight or intelligence.