Zakat is the fourth pillar of Islam and we need to complete this duty in Ramadan. You can read more here What is Zakat. The basic purpose of Zakat is we need to spend part of our money that we hold from longer then a year to poor people.
There are some details in calculating your Zakat amount that is not a problem now. You can calculate your Zakat online with real accuracy and without lot time consuming.

Without further delay, here is a list of free online Zakat calculators in the market.

1) YesPakistani zakat Calculator
2) Islamicity Zakat Calculator
3) Hadiya Foundation Zakat Calculator
4) SoundVision Zakat Calculator

Choose which ever you like more and suites your requirements. Remember that these calculators are based on US Dollar calculation, so keep that in mind while entering amount.

Now you can calculate more efficiently, but if any problem then its better to contact your mosque Imam for detailed guidance and understanding, as 1 by 1 meetings always a best way to learn then  any other thing.