user87937: I am trying to get real fee per trasnaction.
So I have an account whit balance 0.06940000 and have a second account with balance 0.00000000.
To get current fee I have run the command
bitcoin-cli getmempoolinfo

and got the mempoolminfee = 0.00001000.
I thought that when I send the 0.06939000 in my account rest balance will 0.00000000. but I got 0.00004860. Actually the fee was  0.0000514.
general question is WhY ? 
Please tell me to understand how is fees working!

user87883: What getmempoolinfo is returning is not the minimum fee to send a transaction, but the minimum rate per kilobyte to send a transaction. Your bitcoin client will take the configured fee and multiply it by the size of the transaction in kilobytes to calculate the actual transaction fee.
The size of a transaction is somewhat difficult to compute (for a person) because it requires understanding the number of inputs that are required to fulfil the transaction, the number of outputs (primary recipients + change address), and the targeted transaction fee (since appropriate fees could eliminate the need for a change address).
There are online fee calculators out there you can use to estimate these, but it is still difficult to completely empty a wallet with a known fee using the straight bitcoin client.

87937: <p>I am trying to get real fee per trasnaction.</p>

<p>So I have an account whit balance <code>0.06940000</code> and have a second account with balance <code>0.00000000</code>.</p>

<p>To get current fee I have run the command</p>

<pre><code>bitcoin-cli getmempoolinfo
</code></pre>

<p>and got the <code>mempoolminfee = 0.00001000</code>.
I thought that when I send the <code>0.06939000</code> in my account rest balance will <code>0.00000000</code>. but I got <code>0.00004860</code>. Actually the fee was  <code>0.0000514</code>.</p>

<p>general question is WhY ? </p>

<p>Please tell me to understand how is fees working!</p>
 87883: <p>What <code>getmempoolinfo</code> is returning is not the minimum fee to send a transaction, but the minimum <strong>rate per kilobyte</strong> to send a transaction. Your bitcoin client will take the configured fee and multiply it by the size of the transaction in kilobytes to calculate the actual transaction fee.</p>

<p>The size of a transaction is somewhat difficult to compute (for a person) because it requires understanding the number of inputs that are required to fulfil the transaction, the number of outputs (primary recipients + change address), and the targeted transaction fee (since appropriate fees could eliminate the need for a change address).</p>

<p>There are online fee calculators out there you can use to estimate these, but it is still difficult to completely empty a wallet with a known fee using the straight bitcoin client.</p>
