diff --git a/src/Services/Attachments/AttachmentManager.php b/src/Services/Attachments/AttachmentManager.php
index f789d3de..bddea30b 100644
--- a/src/Services/Attachments/AttachmentManager.php
+++ b/src/Services/Attachments/AttachmentManager.php
@@ -160,7 +160,7 @@ class AttachmentManager
 
         $sz = 'BKMGTP';
         $factor = (int) floor((strlen((string) $bytes) - 1) / 3);
-
-        return sprintf("%.{$decimals}f", $bytes / 1024 ** $factor).@$sz[$factor];
+        //Use real (10 based) SI prefixes
+        return sprintf("%.{$decimals}f", $bytes / 1000 ** $factor).@$sz[$factor];
     }
 }
diff --git a/src/Twig/FormatExtension.php b/src/Twig/FormatExtension.php
index 87c906b1..36a8dad4 100644
--- a/src/Twig/FormatExtension.php
+++ b/src/Twig/FormatExtension.php
@@ -119,6 +119,7 @@ final class FormatExtension extends AbstractExtension
     {
         $size = ['B','kB','MB','GB','TB','PB','EB','ZB','YB'];
         $factor = floor((strlen((string) $bytes) - 1) / 3);
-        return sprintf("%.{$precision}f", $bytes / pow(1024, $factor)) . ' ' . @$size[$factor];
+        //We use the real (10 based) SI prefix here
+        return sprintf("%.{$precision}f", $bytes / (1000 ** $factor)) . ' ' . @$size[$factor];
     }
 }