This video will show you how to find your transaction size in kb, so you can calculate your transaction fee, but also show how you can select certain bitcoins to send to lower your fee.
First, go to your bitcoin core installation, go to settings, and then options. Then the wallet tab, and then enable coin control operations.
This will make a new box appear on your send tab, titled coin control.
If you hit inputs there, you will see a list of all of your BTC in your wallet, as seperate inputs. Each one you select will increase your transaction size, and also your fee. You can use this to tailor how much you send to get the lowest fee.
There is also the change listing, where this is the difference between what you selected there, and the amount you input to send.
The fee is also based on what you set as a fee at the bottom, it just shows you more calculations for how it is found, and the total fee.
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