diff --git a/src/carrier.rs b/src/carrier.rs
index ca91abe..0fd3afd 100644
--- a/src/carrier.rs
+++ b/src/carrier.rs
@@ -885,6 +885,22 @@ impl DavFileSystem for CarrierFs {
             Ok(())
         })
     }
+
+    fn get_quota(&self) -> FsFuture<'_, (u64, Option<u64>)> {
+        Box::pin(async move {
+            self.touch();
+            let inner = self.inner.lock().unwrap_or_else(|e| e.into_inner());
+            let total_capacity = inner.manifest.total_blocks as u64 * crate::crypto::CHUNK_SIZE as u64;
+            let used_bytes = inner
+                .manifest
+                .inodes
+                .values()
+                .filter(|i| !i.is_dir)
+                .map(|i| i.size)
+                .sum::<u64>();
+            Ok((used_bytes, Some(total_capacity)))
+        })
+    }
 }
 
 /// Datei-Handle für Dateien innerhalb des Carrier-Dateisystems mit Streaming und Chunk-Pufferung.
diff --git a/src/storage.rs b/src/storage.rs
index a9867e3..ca54f28 100644
--- a/src/storage.rs
+++ b/src/storage.rs
@@ -349,6 +349,38 @@ impl Database {
         self.conn()
     }
 
+    /// Ermittelt den physischen Dateipfad des geöffneten Containers aus SQLite (sofern nicht in-memory).
+    pub fn container_path(&self) -> Option<std::path::PathBuf> {
+        let conn = self.conn();
+        let path_str: String = conn
+            .query_row("PRAGMA database_list;", [], |r| r.get(2))
+            .ok()?;
+        if path_str.is_empty() {
+            None
+        } else {
+            Some(std::path::PathBuf::from(path_str))
+        }
+    }
+
+    /// Ermittelt die physische Dateigröße des Containers über die SQLite-Page-Statistik (Z-04).
+    pub fn get_container_file_size(&self) -> Result<u64> {
+        let conn = self.conn();
+        let page_count: i64 = conn.query_row("PRAGMA page_count;", [], |r| r.get(0))?;
+        let page_size: i64 = conn.query_row("PRAGMA page_size;", [], |r| r.get(0))?;
+        Ok((page_count.saturating_mul(page_size)).max(0) as u64)
+    }
+
+    /// Ermittelt die kumulierte Dateigröße aller im Container gespeicherten Nutzdateien (Z-04).
+    pub fn get_total_used_size(&self) -> Result<u64> {
+        let conn = self.conn();
+        let total: i64 = conn.query_row(
+            "SELECT COALESCE(SUM(size), 0) FROM nodes WHERE is_dir = 0",
+            [],
+            |r| r.get(0),
+        )?;
+        Ok(total.max(0) as u64)
+    }
+
     /// Erzeugt eine geklonte Instanz mit einer isolierten aktiven Session (Slot & DEK).
     pub fn with_session(&self, slot_id: u32, dek: Zeroizing<[u8; 32]>) -> Self {
         Self {
diff --git a/src/vfs.rs b/src/vfs.rs
index 0bee7b8..b91ba7e 100644
--- a/src/vfs.rs
+++ b/src/vfs.rs
@@ -1127,10 +1127,28 @@ impl DavFileSystem for SanctumFs {
     }
 
     fn get_quota(&self) -> FsFuture<'_, (u64, Option<u64>)> {
+        if let Some(ref cfs) = self.carrier_fs {
+            return cfs.get_quota();
+        }
+
         Box::pin(async move {
-            // Virtueller Speicherplatz für Explorer: 1 TB
-            let total_capacity: u64 = 1024 * 1024 * 1024 * 1024;
-            Ok((0, Some(total_capacity)))
+            self.touch();
+            // Z-04: Echte Containergröße (physisch auf Disk) und freier Host-Speicher
+            let container_size = self.db.get_container_file_size().unwrap_or(0);
+            let used_bytes = if container_size > 0 {
+                container_size
+            } else {
+                self.db.get_total_used_size().unwrap_or(0)
+            };
+
+            let free_host_space = self
+                .db
+                .container_path()
+                .and_then(|p| crate::windows::get_available_disk_space(&p))
+                .unwrap_or(1024 * 1024 * 1024 * 1024); // Fallback: 1 TB
+
+            let total_capacity = used_bytes.saturating_add(free_host_space);
+            Ok((used_bytes, Some(total_capacity)))
         })
     }
 }
diff --git a/src/windows.rs b/src/windows.rs
index 403df65..52cadf3 100644
--- a/src/windows.rs
+++ b/src/windows.rs
@@ -846,6 +846,55 @@ pub fn is_process_alive(pid: u32) -> bool {
     }
 }
 
+/// Ermittelt den verfügbaren freien Speicherplatz auf dem Dateisystem des angegebenen Pfads (Z-04).
+pub fn get_available_disk_space<P: AsRef<std::path::Path>>(path: P) -> Option<u64> {
+    #[cfg(windows)]
+    {
+        use std::os::windows::ffi::OsStrExt;
+        let p = path.as_ref();
+        let dir = if p.is_dir() {
+            p.to_path_buf()
+        } else {
+            p.parent().map(|parent| parent.to_path_buf()).unwrap_or_else(|| p.to_path_buf())
+        };
+        let mut wide: Vec<u16> = dir.as_os_str().encode_wide().collect();
+        wide.push(0);
+
+        let mut free_bytes_available = 0u64;
+        let mut total_number_of_bytes = 0u64;
+        let mut total_number_of_free_bytes = 0u64;
+
+        extern "system" {
+            fn GetDiskFreeSpaceExW(
+                lpDirectoryName: *const u16,
+                lpFreeBytesAvailableToCaller: *mut u64,
+                lpTotalNumberOfBytes: *mut u64,
+                lpTotalNumberOfFreeBytes: *mut u64,
+            ) -> i32;
+        }
+
+        let success = unsafe {
+            GetDiskFreeSpaceExW(
+                wide.as_ptr(),
+                &mut free_bytes_available,
+                &mut total_number_of_bytes,
+                &mut total_number_of_free_bytes,
+            )
+        };
+
+        if success != 0 {
+            Some(free_bytes_available)
+        } else {
+            None
+        }
+    }
+    #[cfg(not(windows))]
+    {
+        let _ = path;
+        Some(1024 * 1024 * 1024 * 1024)
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
diff --git a/tests/mount_security_test.rs b/tests/mount_security_test.rs
index 49c0f1c..496b845 100644
--- a/tests/mount_security_test.rs
+++ b/tests/mount_security_test.rs
@@ -242,4 +242,73 @@ fn test_z01_decoy_password_zeroize_memory() {
     drop(ephemeral);
 }
 
+#[tokio::test]
+async fn test_z04_webdav_quota_report() {
+    use dav_server::fs::DavFileSystem;
+    use sanctum::vfs::SanctumFs;
+
+    let temp_dir = std::env::temp_dir();
+    let container_path: PathBuf =
+        temp_dir.join(format!("test_z04_quota_{}.sanctum", std::process::id()));
+    if container_path.exists() {
+        let _ = std::fs::remove_file(&container_path);
+    }
+
+    let salt = generate_salt();
+    let kdf_params = KdfParams {
+        memory_cost: MIN_MEMORY_COST_KIB,
+        time_cost: MIN_TIME_COST,
+        parallelism: 1,
+    };
+    let kek = derive_kek("TestPassZ04!", &salt, &kdf_params).unwrap();
+    let dek = generate_dek();
+    let (wrapped_dek, nonce, tag) = wrap_dek(&kek, &dek).unwrap();
+
+    let db = Database::open(&container_path).unwrap();
+    db.init_schema(&salt, &kdf_params, &wrapped_dek, &nonce, &tag)
+        .unwrap();
+
+    // Erstelle einen Testknoten mit Chunks
+    let node = db.create_node(1, "payload.bin", false).unwrap();
+    let dummy_chunk = vec![0xAAu8; 1024 * 1024]; // 1 MiB
+    db.write_chunk_and_update_size(
+        node.id,
+        0,
+        0,
+        &[0u8; 12],
+        &[0u8; 16],
+        &dummy_chunk,
+        1024 * 1024,
+        123456,
+    )
+    .unwrap();
+
+    let fs = SanctumFs::new(db.clone(), dek, sanctum::crypto::FORMAT_VERSION);
+
+    // Rufe WebDAV get_quota ab
+    let (used, total_opt) = fs.get_quota().await.unwrap();
+
+    assert!(
+        used > 0,
+        "Z-04: Verwendeter Speicherplatz muss > 0 sein (gemeldet: {} Bytes)",
+        used
+    );
+    assert!(
+        total_opt.is_some(),
+        "Z-04: Gesamtkapazität muss gemeldet werden"
+    );
+    let total = total_opt.unwrap();
+    assert!(
+        total >= used,
+        "Z-04: Gesamtkapazität ({}) muss mindestens dem belegten Speicher ({}) entsprechen",
+        total,
+        used
+    );
+
+    drop(fs);
+    drop(db);
+    let _ = std::fs::remove_file(&container_path);
+}
+
+