Setting 6x6 posts in concrete
Your math looks right on. I couldn't verify the concrete but it looked pretty similar to other stuff I've used.
The 12&quot; Sonotube seems small for a 6x6 post. Their site recommends three time the post width so that would mean an 18&quot; Sonotube. you might want to look into that. that means you have to do your calculations for concrete over again.. lol