The smallest units in the universe

When we talk about tiny distances, we often mention millimeters, micrometers, or nanometers. But physics goes far beyond that. The Planck length is considered the smallest meaningful unit of length in the universe.

What is the Planck length?

The Planck length is about 1.6 × 10⁻³⁵ meters: an incredibly small distance that is far beyond what we can currently measure or observe. Below this scale, our usual ideas about space and distance stop working properly.

Why it matters in physics

The Planck length sits at the boundary between:

• Quantum mechanics, which describes very small particles
• General relativity, which describes gravity and large-scale structure

Many theories suggest that at this scale, space itself may be “quantized,” and new physics is needed to understand what really happens.

Smaller than small

Ideas like strings in string theory or a foamy structure of spacetime are attempts to describe what might exist at or below the Planck scale. These concepts are still theoretical and not yet proven.

Curious how small a nanometer or micrometer is in everyday terms? Explore our length converter to compare tiny and large distances.