Calculating alcohol oz addition

[Devin Trudgen]

Hi, hope this is correct thread to post this question. Apologize if not.

My wife has requested one of those hard seltzer drinks (i.e. truly) for her bday. I have decided to just go the easy route the first time and carb up some water and vodka.

Question is amount of vodka to add to get ~5% abv. I figured that 5 gal batch is 640oz and 5% would be 32oz of vodka. However, if the bottle of vodka is 40% abv I would need to add more then 32oz of vodka, correct? I would actually need 80oz of vodka at 40% to achieve 5% abv for the 5gal batch. Is this correct? Thanks for the math help!

 

[Gnomebrewer]

If the vodka is 40%, you need to dilute it with 7 parts water to get 5%. So it's a 1:7 ratio.
640oz / 8 = 80oz, so you need 80oz of vodka and 560oz of water.

I don't know much about selzer drinks, but vodka with water sounds disgusting to me!

 

[Devin Trudgen]

Right so 80oz vodka plus 560oz water equals 640oz (5gal). Thanks