Definition:Ceiling Function/Definition 3

Definition
Let $x$ be a real number.

The ceiling function of $x$ is the unique integer $\left\lceil{x}\right\rceil$ such that:
 * $\left\lceil{x}\right\rceil - 1 < x \le \left\lceil{x}\right\rceil$

Also see

 * Real Number lies between Unique Pair of Consecutive Integers
 * Equivalence of Definitions of Ceiling Function