A WMS is designed to automate, optimise and improve warehouse operations, whereas Enterprise Resource Planning (ERP) is the automation of processes across all areas of a business, from human resources to procurement.
WMS can be used for both small and large warehouses but comes into its own with floors of over 20,000 square feet and the demands placed upon start to get complex. At this level and above it is sometimes referred to as an ERP system or enterprise resource planning.