The waterproofing rating on a tent indicates the capacity of the fabric to resist water pressure (as per the quality and type of fabric used) and is measured in “millimeters (mm)”. The average range is from 1000 mm to 10,000 mm. The minimum rate is 800 mm-1000 mm. The rating is determined through the hydro-static test. Bigger the number, the higher the capacity to withstand greater amounts of water pressure.