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The Universal Coolness Index (UCI) is a formula that evaluates each number according to its interesting properties. The UCI has a maximum of 100.0, and its minimum depends on the number of properties being tested. Currently, the lowest UCI on record is under 12.5%.

A number cannot score 0% on the UCI because, by definition, it becomes cool as soon as it is identified as the "least cool" number.

The formula for the UCI is well-protected though curious number crunchers are invited to attempt to reverse engineer it.

Cool Numbers currently defines six tiers of coolness. The tier that a particular number falls into depends on its UCI score.

  1. Extremely cool (Hall of Fame material): 99% or higher.
  2. Very cool (Gallery material): 95.0% - 98.9%
  3. Cool: 90% - 94.9%
  4. Almost cool: 75% - 89.9%
  5. So-so: 50.0% - 74.9%
  6. Definitely uncool: 49.9% or lower.

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