why your conversion rate is more than 100%

Having a problem with conversion tracking? On this page, I'll guide you to a solution for your campaign having more than 100% conversion rate.

Your conversion rate is the number of conversions divided by the number of clicks on your ad. Since clicks should exceed conversions, your conversion rate typically won't exceed 100%.

Here are some possible reasons why your conversion rate is more than 100%:

Reason 1: A user may leave your website after triggering one conversion and then re-visit your site at another time. If another transaction occurs without another click on your AdWords ad, two conversions would be registered instead of one.

Reason 2: Your conversion rate may exceed 100% if the conversion tracking cookie isn't updated properly by the user's browser when a user visits your site. In this case, more than one conversion may be registered for a single click. It isn't possible to prevent this situation, but please be assured that it occurs very rarely.

For example, a user may arrive at your website after clicking on your ad. After advancing through your site and triggering a conversion, the user may click on the back button to return to the page where the conversion tracking code is placed. In this case, instead of recording one click and one conversion with multiple transactions, the system records one click and multiple conversions with one transaction each.

Reason 3: You may at times see a conversion but no click associated with it. This could happen when a click comes from a blacklisted IP address or is filtered out and somehow our system still records the conversion. If you make a campaign report for the day you should see there's an invalid click registered. The conversion was not charged since there's no click and associated cost for the recodred conversion. You can see this in the keyword performance report for this keyword.

Source: 

http://support.google.com/adwords/bin/answer.py?hl=en&answer=145449