It varies, but it's probably around 6 or 7 SBD today. But it's not a good idea to send such a small amount now, because most of if it would just go to paying the fixed bitcoin transaction fee and you would get very little bitcoin . That's why I recommend using a minimum of 20 SBD (and even more if you have it).
If you want to see the minimum amount at any given time, you can put 0.000001 into the "Receive" amount of the estimator on our web page. Currently it's estimating you would need to send 6.76 SBD, for example to get this very small amount of bitcoin.