How to sync multiple Google calendars on my iPhone is something I have tried to set up for years,
I have always used Google as my calendar and also for my cloud based email system, and like millions of other people I have always carried around an iPhone.
Unfortunately it seamed that only my main Google calendar was visible on my iPhone at any time and this drove me mad.
I like many other people who use multiple PC’s and need a cloud based email solution, I use Google for this and I have multiple colour coded Google calendars each displaying different information.
In a perfect world where the iPhone and Google are friends I would be able to sync multiple Google calendars with my iPhone and turn on and off each calendar from my iPhone when I do or do not want to display them, or when I want to focus on a specific project.
I finally found a way to sync multiple Google calendars with my iPhone or my iPad and it couldn’t be more simple.
Step 1. Google iPhone Calendar Sync, Set up an account.
If you haven’t already done so set up a Gmail account on your iPhone.
Add your account details to access your Google account.

Step 2. Google iPhone Sync Calendar Sync, Turn on your Calendar.

If you havn’t already done so go back into the account you have just set up have and toggle the calendar settings to on.

Step 3. Google iPhone Calendar Sync, Set up Google. 

Next Google needs to be set up so that it will allow you to sync multiple calendars, it couldn’t be easier. All you need to do is follow this link to Google that allows you to sync any of your preferred Google calendars, www.google.com/calendar/iphoneselect

You may be prompted to sign into your Google account, then you will see a list of all your Google calendars, all you have to do is check the boxes of the calendars you want to sync.
In Summary.
This 3 step process will give you access to all of your Google calendars and total control over which ones to display on your iPhone.