title: Are S3 storage costs based on total current usage or on total volume ingested
body: <p>Suppose I have a script which uploads a 100GB object every day to my S3 bucket. This same script will delete any file older than 1 week from the bucket. How much will I be charged at the end of the month?</p>
  
  <p>Let's use pricing from the <code>us-west-2</code> region. Suppose this is a 30-day month and I start with no data in the bucket at the beginning of the month.</p>
  
  <ol>
  <li>If charged for maximum bucket volume per month, I would have 700GB at the end of the month and be charged $0.023 * 7 * 100 = $16.10. Also some money for my PUT requests ($0.005 per 1,000 requests so effectively 0).</li>
  <li>If charged for total amount of data that had transited through the bucket over the course of that month, I would be charged $0.023 * 30 * 100 = $69. (again +effectively $0 for PUT requests)</li>
  </ol>
  
  <p>I'm not clear on which of these two cases Amazon bills. This becomes very important for me, since I expect to have a high amount of churn in my bucket.</p>