Usage meters are essential tools in any usage-based billing system, converting raw data into billable metrics to accurately charge customers for the services they consume. Key functions of a usage meter include real-time data capture, data filtering, transformation, aggregation, handling idempotency and deduplication, supporting flexible pricing rules, time-series usage reporting, SQL query builder for external data sources, and real-time usage monitoring and feedback. By incorporating these features, businesses can maintain accurate billing, ensure transparency for customers, and scale efficiently as usage grows.