.htm page to .html do I need to 301 all old pages..

I have a old site which has been indexed for 3-4 years the old layout sucked so I have a new layout which I have made.

What I am worried about is the old layout is in .htm format and the new layout is in .html format??

Stupid question possibly but will I need to 301 all the htm pages to html or will Google and other search engines just see them as the same thing?

Thanks =)

redirect/rewrite the sites from htm to html with a 301 redirect

edit: ( i dont tested these examples )