# Request Unit (RU)

+ Request Unit (RU) 
  + Is a unified abstraction unit in TiDB for system resources
  + Includes CPU, IOPS, and IO bandwidth metrics
  + Indicate the amount of resources consumed by a single request


| Resource Type                  | RU Consumption                                |
| :----------------------------- | :-------------------------------------------- |
| Read                           | 2 storage read batches consume 1 RU           |
|                                | 8 storage read requests consume 1 RU          |
|                                | 64 KiB read request payload consumes 1 RU     |
| Write                          | 1 storage write batch consumes 1 RU           |
|                                | 1 storage write request consumes 1 RU         |
|                                | 1 KiB write request payload consumes 1 RU     |
| SQL CPU                        | 3 ms consumes 1 RU                            |

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Request Unit (RU) is a unified abstraction unit in TiDB for system resources, which currently includes CPU, IOPS, and IO bandwidth metrics. It is used to indicate the amount of resources consumed by a single request to the database. The number of RUs consumed by a request depends on a variety of factors, such as the type of operations, and the amount of data being queried or modified.

+ Each write operation is eventually replicated to all replicas (by default, TiKV has 3 replicas). Each replication operation is considered a different write operation.
+ In addition to queries executed by users, RU can be consumed by background tasks, such as automatic statistics collection.
+ The preceding table lists only the resources involved in RU calculation for TiDB Self-Hosted clusters, excluding the network and storage consumption. For TiDB Serverless RUs, see TiDB Serverless Pricing Details.