AWS DynamoDB table sizes aren't reported to CloudWatch. This fixes that. Metrics are published hourly to the dynamosize namespace.

You have two options. The first is deploying the following CloudFormation template:

Transform: AWS::Serverless-2016-10-31

Resources:
  App:
    Type: AWS::Serverless::Application
    Properties:
      Location:
        ApplicationId: arn:aws:serverlessrepo:us-east-1:607481581596:applications/dynamosize
        SemanticVersion: 0.1.0

The second option is clicking this link to open the AWS web console, then click the Deploy button.

I personally deploy the above CloudFormation template to all accounts and regions in my AWS org using service-managed CloudFormation stack sets. For that you need to deploy stackset.yml.