SEO Title Tag Length
Presently there are 65 characters available for use safely within meta titles when it comes to SEO, some argue that you can get away with 70. Be on the safe side and go in with 65, over optimised title tags can go noticed too, so be careful.
One other thing to note with meta title tags are that they shouldn’t be duplicated through your site, try to keep the beginning of each title on every page unique, especially the beginning part.
If you are trying to rank for a key term such as “body building”, an appropriate title of the home page could possibly be “Body Building Information | Muscle Growth | Supplements”. But if you have an inner page within the site which is about body building in more depth, selecting a title tag as such “Body Building Details | ….” may not be suitable, try to go for an alternate word and not saturate your sites title tags with primary keywords.
The problem in commerce sites
Avoiding title tag duplication within an e-commerce, or stock related site can be tricky, especially when you have numerous items which are of similar make and model. Best thing to do here is to optimise each title best for the item, if the first keyword in the title tag is duplicated, don’t over worry, just make sure the content on each page is unique as well as the rest of the title tag.