diff --git a/README.md b/README.md
index 416d4d0..4db5c20 100644
--- a/README.md
+++ b/README.md
@@ -10,7 +10,7 @@ Simple key-value store for single-user applications.
 
 ## Cons
 
-* Index stored in memory (`map[key hash (28 bytes)]file offset (int64)`)
+* Index stored in memory (`map[key hash (28 bytes)]file offset (int64)`) - average 200-250 Mb of RAM per 1M keys
 * Need to read the whole file on store open to create file index
 * No way to recover disk space from deleted records
 * Write/Delete operations block Read and each other operations