When I wrote Windows Azure Platform for Enterprises in MSDN magazine in February 2010, the Azure Storage monthly cost under the header Cost Oriented Architecture for the Cloud was erroneous. This was partly due to the lack of detailed understanding of the Storage pricing at that time. The following paragraph requires correction:

“Windows Azure platform pricing is straightforward with the one exception of storage used by Blobs and Tables. An account’s Windows Azure Storage usage is measured each day during a billing cycle and a daily average is computed. The charge will be computed by multiplying this daily average by $0.15/GB. For example if you store 20GB on day one, add 10GB on day two, add 5GB on day three, and delete 5GB on day four, with no activity during the rest of the billing cycle, the price will be computed as shown below:

((20 +10 + 5 – 5)/30) * 0.15 = $0.15”

Correction 1: For the usage scenario described above during the first month, the table below shows the incremental storage used and the daily averages:

Day #

Incremental Daily Usage Avg Daily Storage
1 + 20 GB 20 GB
2 + 10 GB 30 GB
3 + 5 GB 35 GB
4 - 5 GB 30 GB
5 - 30 + 0 GB 30 GB
Total   895 GB

Daily average over the current month (assuming 30 day month) = 895/30 = 29.83 GB.

Storage bill at the end of the month = 29.83 * $0.15 = $4.47/month

Correction 2: The above paragraph hints that Azure Queue pricing strategy is somehow different from Blobs and Tables which is not true. The pricing scheme described in Correction 1 is equally be applicable for Azure Queues.

For more information on Azure Storage pricing at a detailed level can be obtained from this fantastic post from Brad Calder: Understanding Windows Azure Storage Billing – Bandwidth, Transactions, and Capacity 

-Hanu