Solution to your problem is "Device Designer". I hope you are using tableau 10. After creating the dashboard, to your left side you will see the Device preview section. You can see that there are already two options available. One is the default and other is Phone.
Click on the Device Preview button and select the type as "Tablet". Select the specific model if its on the list. Click on the "Add Tablet Layout". This will add up one more options as "Tablet" where default and phone is mentioned. Now Click on Phone/ Default/ tablet to see one dashboard in different resolutions. Please refer to the below screenshot for the same.
Let me know if this helps.
Thanks and Regards,
The dashboard to be viewed in server not in desktop version and currently are using Tableau version 9.2.
Thanks & Regards,
Above settings that I have mentioned are set in tableau desktop which are used by tableau server while rendering the tableau dashboard (Tablea userver 10 only).
In your case, you will have to format entire dashboard again by keeping the resolution in mind for Ipad or any other deivce. In tableau 10, this new feature is added, so that user will not have to create the separate dashboard and maintain the same.