How can I get the size of an Amazon S3 bucket?

In the CLI you can list recursively and summarize in a human readable format.

aws s3 ls s3://mybucket --recursive --human-readable --summarize
... [snipped output] ...
Total Objects: 46
   Total Size: 29.5 MiB

Using the BucketSizeBytes CloudWatch Metric (ref: https://docs.aws.amazon.com/AmazonS3/latest/userguide/metrics-dimensions.html) is probably your best bet - and being it CloudWatch, you can also alarm on size, use triggers etc as you would do with any other metric.

Need to be careful though, this metric might be a few hours behind.

In the S3 console you can go navigate to your bucket and select all objects in the bucket. Once all objects are selected you can go to "Actions" > "Calculate total size" Hope that helps

There are alternative ways.

• Cloudwatch Metrics.
• Cost Explorer API, UI or Billing.
• Generate an S3 Inventory, use Athena to run query to sum sizes. Might be overkill though, but you can filter as you wish if you need more than just the usage data.