How long will your experiment take?
This is the number of people visiting your site that could see the change on a given day.
This is the percentage of your eligible visitors that currently complete your goal (e.g. purchasing or signing up).
This is the percent by which you predict you will change your base conversion rate. Use the minimum that would be worth the effort, or play with different values.
If you are 95% confident in a result, this implies that with 5% probability the observed difference is in fact due to chance.