No worries there is a free service which connects to your gmail account and gives you a monthly usage statistic reports. Its called Gmailmeter. Gmailmeter gives you a stats regarding how many emails did you received, sent, deleted etc. It also shows you longest conversations in emails. Whom you email a lot and many more statistic reports. Its a helpful report which tracks and shows your gmail usage. You can visit www.gmailmeter.com and sign in for a free account.