Three admin pages, three different numbers, and a director asking why "we pay for a terabyte" is not enough. This is the model, in one place.
The pool
Your tenant gets 1 TB, plus 10 GB for every eligible licensed user, as one shared pool for every SharePoint site (including the sites behind Teams). OneDrive is separate: each user has their own 1 TB (or more) that does not touch the pool.
Eligible means most business and enterprise plans (Business Basic/Standard/Premium, E3, E5, and their government and education equivalents). Frontline F1/F3 licences add nothing. A 500-user company with 300 office staff and 200 frontline workers has 1 TB + 3 TB = 4 TB, not 6 TB.
Extra storage is bought as Office 365 Extra File Storage, per GB per month, and simply enlarges the pool.
Site quotas
Within the pool, storage is either automatic (every site can grow until the pool is exhausted; the default) or manual (each site gets a quota; a site at its quota goes read-only for new content while the rest of the tenant keeps working). Manual is more work and much safer: one site of daily exports cannot take the whole company read-only.
Connect-SPOService -Url https://contoso-admin.sharepoint.com
Set-SPOTenant -SiteStorageQuotaMode Manual # or Automatic
Set-SPOSite -Identity https://contoso.sharepoint.com/sites/Exports -StorageQuota 51200 -StorageQuotaWarningLevel 46080 # MBWhat counts
Everything on the site: current file content, every version of every file, both recycle bins, the Preservation Hold Library (if retention applies), list items and attachments, pages and site assets. The number in the admin centre is the sum of all of it.
What people think counts: the files they can see in the document library. That is usually the smallest part.
Why three pages disagree
- Document library view shows current file sizes only. No versions, no bins. Always the lowest number.
- Storage Metrics (
/_layouts/15/storman.aspx) shows every library and list on the site collection with totals that include versions, and lets you drill to files. Updated by a periodic crawl. - SharePoint admin centre → Active sites shows the site total, which is what counts against the pool, updated every 24–48 hours.
- Get-SPOSite StorageUsageCurrent is the admin centre number in MB.
They are all "right"; they measure different things at different times. When you need one number to act on, use the admin centre total; when you need to know why, use Storage Metrics.
Things that do not count
- Deleted sites in the admin centre recycle bin (93 days) — not counted while there.
- Files in Microsoft 365 Archive — moved to cold storage at a lower price, out of the pool.
- OneDrive content, Exchange mailboxes, Teams chat.
The conversation with the director, in three lines
- We have N TB because of X eligible licences; frontline staff do not add to it.
- The three biggest sites are A, B, C; on those, versions and recycle bins are Y% of the total.
- We can reclaim Z TB with a version trim and by emptying second-stage bins before we buy anything, and put manual quotas on the export sites so this does not recur.
Filling in Y and Z is the job Storage Analyzer does for free on any site: what you can see versus what you are storing, versions estimated, the remainder attributed to bins and hold library, libraries ranked. Pair it with the twenty-minute triage.