diff --git a/rustcryptfs-lib/src/content_enc.rs b/rustcryptfs-lib/src/content_enc.rs
index ed94ff3..702bcbd 100644
--- a/rustcryptfs-lib/src/content_enc.rs
+++ b/rustcryptfs-lib/src/content_enc.rs
@@ -69,4 +69,33 @@ impl ContentEnc {
 
         return Ok(buf.to_vec());
     }
+
+    pub fn get_real_size(encrypted_size: u64) -> u64 {
+        if encrypted_size == 0 {
+            0
+        } else {
+            let x = (encrypted_size - 50) / 4128;
+
+            let y = (encrypted_size - 50) - x * 4128;
+            x * 4096 + y
+        }
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::ContentEnc;
+
+    #[test]
+    fn test_get_real_size() {
+        assert_eq!(0, ContentEnc::get_real_size(0));
+
+        for real_size in 1..4096 * 4 + 1 {
+            let nbr_full_blocks = real_size / 4096;
+            let encrypted_size =
+                18 + nbr_full_blocks * (4096 + 32) + real_size - nbr_full_blocks * 4096 + 32;
+
+            assert_eq!(real_size, ContentEnc::get_real_size(encrypted_size));
+        }
+    }
 }
diff --git a/rustcryptfs-linux/src/encrypted_filesystem.rs b/rustcryptfs-linux/src/encrypted_filesystem.rs
index 7b340ce..e858a88 100644
--- a/rustcryptfs-linux/src/encrypted_filesystem.rs
+++ b/rustcryptfs-linux/src/encrypted_filesystem.rs
@@ -10,7 +10,7 @@ use std::{
 };
 
 use fuser::{FileAttr, FileType, Filesystem, FUSE_ROOT_ID};
-use rustcryptfs_lib::GocryptFs;
+use rustcryptfs_lib::{content_enc::ContentEnc, GocryptFs};
 
 use crate::{
     error::Result,
@@ -49,17 +49,6 @@ impl EncryptedFs {
         fuser::mount2(self, mountpoint, &[]).unwrap();
     }
 
-    fn get_real_size(size: u64) -> u64 {
-        if size == 0 {
-            0
-        } else {
-            let x = (size - 50) / 4128;
-
-            let y = (size - 50) - x * 4128;
-            x * 4096 + y
-        }
-    }
-
     fn get_file_type(file_type: StdFileType) -> FileType {
         if file_type.is_file() {
             FileType::RegularFile
@@ -93,7 +82,7 @@ impl EncryptedFs {
         let file_type = Self::get_file_type(meta.file_type());
 
         let file_size = if meta.is_file() {
-            EncryptedFs::get_real_size(meta.size())
+            ContentEnc::get_real_size(meta.size())
         } else {
             meta.size()
         };