diff --git a/@xen-orchestra/backups/RemoteAdapter.mjs b/@xen-orchestra/backups/RemoteAdapter.mjs
index 8ab8bc1e894..1905a4e6a50 100644
--- a/@xen-orchestra/backups/RemoteAdapter.mjs
+++ b/@xen-orchestra/backups/RemoteAdapter.mjs
@@ -18,6 +18,7 @@ import fromEvent from 'promise-toolbox/fromEvent'
 import groupBy from 'lodash/groupBy.js'
 import pDefer from 'promise-toolbox/defer'
 import pickBy from 'lodash/pickBy.js'
+import reduce from 'lodash/reduce.js'
 import tar from 'tar'
 import zlib from 'zlib'
 
@@ -826,6 +827,29 @@ export class RemoteAdapter {
     }
     return metadata
   }
+
+  #computeTotalBackupSizeRecursively(backups) {
+    return reduce(
+      backups,
+      (prev, backup) => {
+        const _backup = Array.isArray(backup) ? this.#computeTotalBackupSizeRecursively(backup) : backup
+        return {
+          onDisk: prev.onDisk + (_backup.onDisk ?? _backup.size),
+        }
+      },
+      { onDisk: 0 }
+    )
+  }
+
+  async getTotalVmBackupSize() {
+    return this.#computeTotalBackupSizeRecursively(await this.listAllVmBackups())
+  }
+
+  async getTotalBackupSize() {
+    const vmBackupSize = await this.getTotalVmBackupSize()
+    // @TODO: add `getTotalXoBackupSize` and `getTotalPoolBackupSize` once `size` is implemented by fs
+    return vmBackupSize
+  }
 }
 
 Object.assign(RemoteAdapter.prototype, {
diff --git a/CHANGELOG.unreleased.md b/CHANGELOG.unreleased.md
index 28f167ebf88..75981509962 100644
--- a/CHANGELOG.unreleased.md
+++ b/CHANGELOG.unreleased.md
@@ -19,6 +19,7 @@
 - [V2V] Fix computation of `memory_static_max`
 - **XO 6**:
   - [Dashboard] Display backup issues data (PR [#7974](https://github.com/vatesfr/xen-orchestra/pull/7974))
+- [REST API] Add S3 backup repository information in the `/rest/v0/dashboard` endpoint (PR [#7978](https://github.com/vatesfr/xen-orchestra/pull/7978))
 
 ### Bug fixes
 
diff --git a/packages/xo-server/src/xo-mixins/rest-api.mjs b/packages/xo-server/src/xo-mixins/rest-api.mjs
index 9daa928a543..b4998938468 100644
--- a/packages/xo-server/src/xo-mixins/rest-api.mjs
+++ b/packages/xo-server/src/xo-mixins/rest-api.mjs
@@ -8,6 +8,7 @@ import { pipeline } from 'node:stream/promises'
 import { json, Router } from 'express'
 import { Readable } from 'node:stream'
 import cloneDeep from 'lodash/cloneDeep.js'
+import Disposable from 'promise-toolbox/Disposable'
 import groupBy from 'lodash/groupBy.js'
 import path from 'node:path'
 import pDefer from 'promise-toolbox/defer'
@@ -226,35 +227,38 @@ async function _getDashboardStats(app) {
   }
 
   try {
-    const remotes = await app.getAllRemotes()
-    const remotesInfo = await app.getAllRemotesInfo()
+    const s3Brsize = { backups: 0 }
+    const otherBrSize = { available: 0, backups: 0, other: 0, total: 0, used: 0 }
 
-    const backupRepositoriesSize = remotes.reduce(
-      (prev, remote) => {
-        const { type } = parse(remote.url)
-        const remoteInfo = remotesInfo[remote.id]
+    const backupRepositories = await app.getAllRemotes()
+    const backupRepositoriesInfo = await app.getAllRemotesInfo()
 
-        if (!remote.enabled || type === 's3' || remoteInfo === undefined) {
-          return prev
-        }
+    for (const backupRepository of backupRepositories) {
+      const { type } = parse(backupRepository.url)
+      const backupRepositoryInfo = backupRepositoriesInfo[backupRepository.id]
 
-        return {
-          available: prev.available + remoteInfo.available,
-          backups: 0, // @TODO: compute the space used by backups
-          other: 0, // @TODO: compute the space used by everything that is not a backup
-          total: prev.total + remoteInfo.size,
-          used: prev.used + remoteInfo.used,
-        }
-      },
-      {
-        available: 0,
-        backups: 0,
-        other: 0,
-        total: 0,
-        used: 0,
+      if (!backupRepository.enabled || backupRepositoryInfo === undefined) {
+        continue
       }
-    )
-    dashboard.backupRepositories = { size: backupRepositoriesSize }
+
+      const totalBackupSize = await Disposable.use(app.getBackupsRemoteAdapter(backupRepository), adapter =>
+        adapter.getTotalBackupSize()
+      )
+      const { available, size, used } = backupRepositoryInfo
+
+      const isS3 = type === 's3'
+      const target = isS3 ? s3Brsize : otherBrSize
+
+      target.backups += totalBackupSize.onDisk
+      if (!isS3) {
+        target.available += available
+        target.other += used - totalBackupSize.onDisk
+        target.total += size
+        target.used += used
+      }
+    }
+
+    dashboard.backupRepositories = { s3: { size: s3Brsize }, other: { size: otherBrSize } }
   } catch (error) {
     console.error(error)
   }