Compute required Sample Size for your A/B tests (A-priori)

So if you want to get started with A/B testing, you should calculate up front if you have enough users and conversions to see if it is even possible to perform an A/B test on your site. There are some general rules of thumb out there that say “don’t go A/B testing when you have < 1000 conversions”, which is fine, but probably not really helpful in your situation.

See http://www.gui.do/post/compute-required-sample-size-for-your-ab-tests for the full article and explainer video.