<p>I think it's around 50 SP to be safe, but I've seen lower.&nbsp;</p>

<p>Littleboy gave them best answer so far, very in-depth.</p>
<p>However, I have to clarify that this steem vote dust threshold is getting removed in the upcoming hard fork, so don't worry too much about it since it reportedly comes in about half a month.</p>
<p>Cheers</p>

<p>I think there's two parts to consider within my answer, how much steem power do you need to be actually able to cast a vote and how much steem power do you need it to provide value.&nbsp;</p>
<p>In terms of how much Steem power do you need to be able to vote and it's successfully be registered to the blockchain, this is all dependent on the amount of bandwidth you have. Bandwidth warrants how much you can transact with the blockchain over a certain amount of time, the amount of bandwidth you have is directly related to the amount of Steem Power you have. The more Steem power, the more bandwidth you will have. In order to have enough bandwidth to be able to vote I would recommend that you keep you Steem power of at least 5, your bandwidth will of course run out quickly and you will often find yourself without enough bandwidth to transact, but regularly you should enough bandwidth to do a few transactions.</p>
<p>In terms of how much Steem power do you need to add value, the answer is quite simple, even the smallest amount of Steem power will provide some value to a post, when you reach ~95 Steem power (at this current time) you will see your votes adds $0.01.&nbsp;</p>