How do I know if tent is waterproof ? How many PU / HH / mm ?

How do I know if tent is waterproof ? How many PU, HH, mm means water resistance ?

Waterproof ratings of tents are measured in Hydrostatic Head (HH) in milimeters (mm).

Tents are usually water resistant rather than waterproof. They can resist the penetration of water to some degree, but not entirely. For example some tents may be resistant against a light rain, but not against the storm or intensive showers.

Basic water resistance of tents against a regular rain starts at 1000mm - 1500mm.