If your Gmail uses the conversation view, then Gmail does not display the number of email messages in your account – it will display the number of conversations. Turning the conversation view off is needed to see the actual number of email messages in your Gmail account.

So here is step by step instructions on how to get the number of email messages in your Gmail account:

1. Turn Gmail conversations view off. The instructions are here.
2. Select All Mail in the label list on the left side of your email. These instructions are here
3. The number of email messages is shown in the upper right corner of your Gmail