1 TB = 1024 GB in SPO?

Anatoly Mironov

There is confusion around how the storage is calculated in SharePoint Online. I believe, in SharePoint Online 1 TB is 1024 GB (based on powers of two), although the SI Prefix is for numbers based on powers of 10 (1TB = 1000GB, Wikipedia). In this post I would like to summarize the results of my investigations and I hope Microsoft or the community can confirm or disconfirm this.

First, let me explain why we care about it. The storage in SharePont is limited and we need to keep an eye on it. Especially in our case, where we need to track storage utilization across different parts of the organization/our tenant. The storage in SharePoint is calculated like so:

1 TB + 10GB * E-licensed users

The tricky part, though, is how to convert it into TB correctly.

Why I believe Microsoft treats 1 TB as 1024 GB

First of all, I can see it clearly in my dev tenant with exactly 25 licenses.

That would give 1TB + 10GB*25 = 1,25 TB if it would be based on powers of 10. But it isn’t because the storage I get is 1,24 TB, or 1,244 to be precise.

That means, for every E-license you get 10 GB or 10/1024 TB.

That also means you need more licenses to get the desired storeage. E.g. 10 TB more storage requires 1024 licenses and not 1000, 10 TB = 10240 GB, 10240 GB / 10 = 1024 E-licenses.

Also in OneDrive, the initial space I get, is 1024 GB (or 1TB). If 1TB = 1024GB in OneDrive, why should SPO be different?

Further, the MSDocs page reveals that the 25 TB are 25600 GB (which is exactly the product of 25 and 1024):

One contradictory page, though is the news about storage increase:

The calculations there are based on the decimal system:

Calculation of MB and GB

Just to verify how the storage is calculated in KB, MB and GB, I looked at the Storage of a SharePoint site. Luckily, I can get the storage used in Bytes, MB and GB (from different sources) and compare them to each other.

When I calculate back and forth I can defnitely see, it is multipled/divided by 1024, hence powers of 2:

The values in blue are the reported values. The other values are calculated.

The values in GB are exactly the same, the Bytes, KB and MB differ a bit due to rounding