Your total kWh usage for the month is printed on your utility bill. This number is the difference between your two meter readings. To calculate your average monthly kWh usage, gather your last 12 utility bills, add up your kWh usage from each bill, and divide the total by 12. If you do not have 12 utility bills, use as many as you have available.
If you have an online account with your utility company, you can access your bills online. Some utilities even feature a graph or table listing your monthly kWh usage.
Alternatively, you can always call your local utility company directly and ask them for your average monthly kWh usage.