Pour costs work by dividing the total bottle price plus tax by the amount of “pours” contained in that bottle and then adding that number to the same number multiplied by your markup percentage.
So, for a 2oz pour of Blanton’s at a 250% markup, you get:

$63.70  /  12.68 pours/btl = $5.02

$5.02 x 2.5 = $12.55 + $5.02 = $17.57

But, WOW, this math is boring, aren’t you glad you have BottleHound? Set as many pour costs as you like. These settings will be relevant throughout the app.