The maximum width and height for a Facebook iFrame page (so that it will not create scroll bars) is:
Width: 490 pixels
Height: 764 pixels
There are 2 good ways of creating an iFrame tab for Facebook. I’m going to call them the easy way and the proper way. There are advantages and disadvantages involved.
Easy Way: iFrames for Pages App (by WildFire)
This application makes it very easy to create Facebook tabs in minutes and comes with a helpful form that lets you create a Facebook iFrame page without any coding knowledge. The downside is that the iFrame page is hosted on WildFire’s shared servers and this makes it difficult to track through Google Analytics.
Proper Way: Facebook Developers App (by Facebook)
This is the true proper way of adding an iFrame tabbed page to your business Facebook page. It takes about 10 minutes to set up and there are a lot of steps. If you are not comfortable with creating HTML pages or Facebook development, you may need assistance with a web designer (contact us). Advantages to this way include proper analytics tracking, complete control over content including shopping cart and e-commerce functionality, as well as a host of others.
Great tutorial: How to Set up a Facebook Custom iFrame Landing Page Application (tutorial from HubSpot)