this code probable help you .
<iframe src="" onload="this.width=screen.width;this.height=screen.height;">
Answering this just in case if someone else like me stumbles upon this post among many that advise use of JavaScripts for changing iframe height to 100%.
I strongly recommend that you see and try this option specified at How do you give iframe 100% height before resorting to a JavaScript based option. The referenced solution works perfectly for me in all of the testing I have done so far. Hope this helps someone.
Source: Stackoverflow.com