Figure out what to include
We recommend that you cover all conceivable expenses in your emergency fund.
Start with the basics. How much do you spend on groceries each month? If you don't know, now is a good time to start tracking that. And if you eat out a lot, you'll either need to include that, or plan on higher grocery bills. If you have pets, include the cost of their food and care in the tab. Unless you're ready to move into your brother-in-law's basement, be sure to cover your rent payments too.
And don't forget utilities--gas, electricity, water, phone, and even cable/satellite and internet.