diff --git a/Usage.md b/Usage.md
index 5a34173..dff5d0c 100644
--- a/Usage.md
+++ b/Usage.md
@@ -256,6 +256,10 @@ stty lnext undef
 | `du` | disk usage |
 | `au` | apparent disk usage |
 
+## File size
+
+The minimum file size unit is byte (B). The rest are K, M, G, T, P, E, Z, Y (powers of 1024), same as the default units in `ls`.
+
 ## Help
 
 ```sh