Leading Zero Counter

About this calculator

Counting leading zeros (CLZ) means counting how many zero bits appear before the first 1-bit in a number's binary representation at a fixed bit width — for example, the 8-bit value 00010110 has 3 leading zeros. It's closely related to finding a number's bit-length and its floor(log₂(n)) value, since the position of the first set bit determines both.

Low-level programmers use CLZ for fast integer log2 calculations, normalizing floating-point mantissas, and bit-manipulation tricks in performance-critical code, which is why most modern CPUs implement it as a single hardware instruction (x86's LZCNT, ARM's CLZ) rather than requiring a software loop — this calculator lets you check that instruction's result by hand.