midCosmos DB
What is Request Unit (RU) in Cosmos DB?
Updated Feb 20, 2026
Short answer
A Request Unit (RU) in Azure Cosmos DB is a performance measurement that represents the cost of database operations like reads, writes, and queries.
Deep explanation
Cosmos DB abstracts computing resources using Request Units (RUs). Every operation consumes RUs depending on its complexity:
- Simple read = low RU cost
- Complex query or large document write = higher RU cost
You provision throughput in RUs per second. If your workload exceeds the provisioned RU/s, requests may be throttled.
Efficient data modeling (small documents, proper indexing, good partitioning) reduces RU consumption and improves performance.
Real-world example
A product catalog app:
- Fetching a single product → 1–5 RUs
- Querying all products in a category → 50–200 RUs depending on data size
Common mistakes
- - Ignoring RU cost while designing queries.
- - Over-provisioning without optimization.
- - Assuming storage and RU are the same metric.
Follow-up questions
- How do you reduce RU consumption?
- What causes RU throttling?
- What is autoscale RU in Cosmos DB?