diff --git a/src/borg/cache.py b/src/borg/cache.py
index 21efcbc9e..cc57e7bc9 100644
--- a/src/borg/cache.py
+++ b/src/borg/cache.py
@@ -20,13 +20,12 @@ from .helpers import format_file_size
 from .helpers import yes
 from .helpers import remove_surrogates
 from .helpers import ProgressIndicatorPercent, ProgressIndicatorMessage
-from .item import Item, ArchiveItem
+from .item import Item, ArchiveItem, ChunkListEntry
 from .key import PlaintextKey
 from .locking import Lock
 from .platform import SaveFile
 from .remote import cache_if_remote
 
-ChunkListEntry = namedtuple('ChunkListEntry', 'id size csize')
 FileCacheEntry = namedtuple('FileCacheEntry', 'age inode size mtime chunk_ids')
 
 
diff --git a/src/borg/helpers.py b/src/borg/helpers.py
index f6247cd38..2bd5f4071 100644
--- a/src/borg/helpers.py
+++ b/src/borg/helpers.py
@@ -1701,10 +1701,12 @@ class ItemFormatter(BaseFormatter):
         return len(item.get('chunks', []))
 
     def calculate_size(self, item):
-        return item.file_size()
+        # note: does not support hardlink slaves, they will be size 0
+        return item.file_size(compressed=False)
 
     def calculate_csize(self, item):
-        return sum(c.csize for c in item.get('chunks', []))
+        # note: does not support hardlink slaves, they will be csize 0
+        return item.file_size(compressed=True)
 
     def hash_item(self, hash_function, item):
         if 'chunks' not in item:
diff --git a/src/borg/item.pyx b/src/borg/item.pyx
index a0b9e3efd..c3125c577 100644
--- a/src/borg/item.pyx
+++ b/src/borg/item.pyx
@@ -1,3 +1,5 @@
+from collections import namedtuple
+
 from .constants import ITEM_KEYS
 from .helpers import safe_encode, safe_decode
 from .helpers import StableDict
@@ -113,6 +115,8 @@ class PropDict:
         return property(_get, _set, _del, doc=doc)
 
 
+ChunkListEntry = namedtuple('ChunkListEntry', 'id size csize')
+
 class Item(PropDict):
     """
     Item abstraction that deals with validation and the low-level details internally:
@@ -172,23 +176,38 @@ class Item(PropDict):
 
     part = PropDict._make_property('part', int)
 
-    def file_size(self, hardlink_masters=None, memorize=False):
-        """determine the size of this item"""
-        size = self.get('size')
-        if size is not None:
-            return size
-        chunks = self.get('chunks')
-        having_chunks = chunks is not None
-        if not having_chunks:
-            # this item has no (own) chunks, but if this is a hardlink slave
-            # and we know the master, we can still compute the size.
-            hardlink_masters = hardlink_masters or {}
-            chunks, _ = hardlink_masters.get(self.get('source'), (None, None))
-            if chunks is None:
-                return 0
-        size = sum(chunk.size for chunk in chunks)
-        if memorize and having_chunks:
-            self.size = size
+    def file_size(self, hardlink_masters=None, memorize=False, compressed=False):
+        """determine the (uncompressed or compressed) size of this item"""
+        attr = 'csize' if compressed else 'size'
+        try:
+            size = getattr(self, attr)
+        except AttributeError:
+            # no precomputed (c)size value available, compute it:
+            try:
+                chunks = getattr(self, 'chunks')
+                having_chunks = True
+            except AttributeError:
+                having_chunks = False
+                # this item has no (own) chunks list, but if this is a hardlink slave
+                # and we know the master, we can still compute the size.
+                if hardlink_masters is None:
+                    chunks = None
+                else:
+                    try:
+                        master = getattr(self, 'source')
+                    except AttributeError:
+                        # not a hardlink slave, likely a directory or special file w/o chunks
+                        chunks = None
+                    else:
+                        # hardlink slave, try to fetch hardlink master's chunks list
+                        # todo: put precomputed size into hardlink_masters' values and use it, if present
+                        chunks, _ = hardlink_masters.get(master, (None, None))
+                if chunks is None:
+                    return 0
+            size = sum(getattr(ChunkListEntry(*chunk), attr) for chunk in chunks)
+            # if requested, memorize the precomputed (c)size for items that have an own chunks list:
+            if memorize and having_chunks:
+                setattr(self, attr, size)
         return size