. in place of ,

If your users are all in Belgium and would assume that "," is the correct separator, you should be able to just set the current culture to your Belgian culture of choice.

If you actually need support for multiple cultures you have a bit more work to do. You'll need to keep track of each user's preferred culture, then use that culture when displaying values in the UI. You should also store information in your database or other data store in the invariant culture. You can use the various item data binding events on the DetailsView to do the preferred culture <-> invariant culture conversions.

Thread.CurrentThread.CurrentUICulture = CultureInfo.InvariantCulture;

Thank you for the answer but that don't work.

If I put 10,25 and save it, the system return 10,25 (that's correct)
If I put 10.25 and save it, the system return 1025 (that's incorrect)

this is the code :

protected void Page_Load(object sender, EventArgs e)
   {
       Thread.CurrentThread.CurrentUICulture = CultureInfo.InvariantCulture;