You can find courses worth 40, 60, 80, 100 hrs. The general perception is that the less hours a course is worth the less is the value of the certificate. It’s got to be said though that employers rarely specify how many hrs a TESL/TEFL Certificate should be worth. What matters to them is that you are certified.
Personally I would recommend that more than the number of hrs attached to a certificate you look at the course content. Start by asking a few providers for their course syllabus and compare them. Check their tutors’ credentials. Make sure the course requires some actual work on your part and it is not based on “Yes or No” answers or “Read This Unit and Summarize It” type of coursework. Try and find out what other students who have taken the course say about it. Basically do as much research as you can.
You could start by taking a look at TEFLWatch
. This is a site where TESL/TEFL courses and course providers are independently reviewed and rated.
With regards to employers’ requirements these vary greatly according to where and at what level you wish to teach. It might be useful to contact a few schools where you’ like to work and ask them for their specific requirements.