What is the UK equivalent of USDA zones?

The UK equivalent of the USDA Hardiness Zones is the Royal Horticultural Society (RHS) Hardiness Rating system, which rates plants based on their ability to survive the minimum winter temperature in a particular region.

The RHS system uses a scale of H1a to H7, with H1a being the most tender and H7 the hardiest. The rating takes into account factors such as temperature, humidity, rainfall, wind and snow cover. The ratings are used to help gardeners select plants that are suitable for their local climate and condition