diff --git a/tools/releasetools/build_image.py b/tools/releasetools/build_image.py
index d775ae8..fbed77d 100755
--- a/tools/releasetools/build_image.py
+++ b/tools/releasetools/build_image.py
@@ -427,7 +427,16 @@
   if (prop_dict.get("use_dynamic_partition_size") == "true" and
       "partition_size" not in prop_dict):
     # If partition_size is not defined, use output of `du' + reserved_size.
-    size = GetDiskUsage(in_dir)
+    # For compressed file system, it's better to use the compressed size to avoid wasting space.
+    if fs_type.startswith("erofs"):
+      tmp_dict = prop_dict.copy()
+      if "erofs_sparse_flag" in tmp_dict:
+        tmp_dict.pop("erofs_sparse_flag")
+      BuildImageMkfs(in_dir, tmp_dict, out_file, target_out, fs_config)
+      size = GetDiskUsage(out_file)
+      os.remove(out_file)
+    else:
+      size = GetDiskUsage(in_dir)
     logger.info(
         "The tree size of %s is %d MB.", in_dir, size // BYTES_IN_MB)
     # If not specified, give us 16MB margin for GetDiskUsage error ...