What is an RU and how are they consumed? RUs measure the cost of both read and write operations against your Cosmos container. Discover more about RUs and Scaling throughput in Azure Cosmos DB. In Azure Cosmos DB, provisioned throughput is represented as request units/second (RU/s, plural: RUs). RUs measure the cost of both read and write operations against your Cosmos container as shown in the image above.
You can provision RUs on a Cosmos container or a Cosmos database. RUs provisioned on a container are exclusively available for operations performed on that container. RUs provisioned on a database are shared among all the containers within that database (except for any containers with exclusively assigned RUs).
For elastically scaling throughput, you can increase or decrease the provisioned RU/s at any time. For more information, see How-to provision throughput and elastically scale Cosmos containers and databases. For globally scaling throughput, you can add or remove regions on your Cosmos account at any time. For more information, see How-to add or remove regions to your Cosmos account. Associating multiple regions with a Cosmos account is important in many scenarios to achieve low latency and high availability around the world.
https://docs.microsoft.com/en-us/azure/cosmos-db/scaling-throughput