Hi there Tsar,
You'd think it would be easier but unfortunately it isn't
. I will try and explain why but before I do please allow me to write one paragraph on the history here.
BIABrewer.info put many hours over many months into trying to help BeerSmith2 be a success. A search here on BeerSmith2 will show you some of the guides that were written here and a glimpse of just how much work went into supporting BeerSmith2. In fact, you'll find the answer to your keg question amongst all that but you will have to do a lot of reading. And that is the problem. There are so many errors and tricks and adjustments and pitfalls in the program, it becomes impossible to educate people into it. For example, there are seven ways that a new BeerSmith user (and probably an old one as well) could scale a recipe but only two of these methods give a correct answer. Although a few very important corrections did get implemented, BIABrewer.info finally gave up as there were so many other critical things that, even today, still remain unchanged.
Here's a few points that might explain why you could be heading into dangerous territory...
1. Fixed versus Variable Efficiency: In BeerSmith and every other brewing software program you have to nominate a fixed 'Brewhouse' efficiency. Even if you set up BeerSmith so that this meant EIK rather than EIF, all your numbers will still be based on incorrect logic as a high gravity beer will give you far lower efficiency of any sort than a low gravity beer. The BIABacus however, adjusts your efficiencies for you. (I am not even going to comment on just how many problems the term 'Brewhouse Efficiency' has caused the entire home-brew community.)
2. Adjusting for Bitterness: There are errors in the Beersmith bitterness formula so you can't really adjust for bitterness accurately. In the BIABacus you can by simply changing the second line of Section D assuming your are using the PR1.3 version.
3. Adjusting for Colour: You should not adjust for colour if you are scaling a recipe. In other words, when scaling a recipe, you want to maintain the ratio for the individual grains. A scaled recipe should very rarely have the same colour value as the original recipe as the formulas are very primitive. Valuing the colour formula when scaling over the grain ratios is a gimmick and is incorrect. Regarding design, if you are designing a recipe, then colour becomes a subsidiary factor to flavour. In other words, colour adjustments need to be made with a full awareness of how the adjustment affects flavour. A program that retains the colour value of a scaled recipe ignores this fact and, after several scalings, the recipe becomes distorted anyway.
4. Access to Quality Recipes: Some commercial software claims that there is a lot of value in having thousands of recipes posted on the net in their format. There's two problems here. Firstly, there is no quality control on the recipes. Anyone, even with no brewing knowledge at all, can post recipes. Secondly, the recipe reports of these programs do not contain enough information for other users to copy/scale them well. While we don't have many recipes yet in BIABacus format, one thing we do know is that any that do get published in that format officially here will be keepers and will be easily scaled/copied by other brewers.
5. Transparency and Education: Commercial software usually has a lot of tabs/windows etc. What happens here is that everything becomes smoke and mirrors. I know because I have triple-checked many formulas in these programs and it takes hours upon hours to find the errors. Behind all that smoke, you actually find very little valuable information. For example, the most critical volume number in brewing, the EOBV-A cannot even be recorded in BeerSmith2 nor can kettle trub. The BIABacus allows for all this.
6. Pre-pitching or post-fermentation: Not even going to go there. There is no comparison at all.
7. Versatility and Simplicity - Have a crack at doing some of the water adjustments you can do in two seconds in Section W of the BIABacus in any other program. Many actually can't be done. There are a lot of things like this that are simple in the BIABacus and impossible in other programs.
So Tsar, I think if you want a program that is really going to serve you then you need to go for the BIABacus (in its humble, simple, spreadsheet form) as it is the only one out there that, how do I say this???... takes responsibility. Any other program, if you don't hit your numbers people will say, well you haven't set this right or that right etc etc. It's more smoke, no logic and no education.
If you want fast, correct answers then learn the BIABacus - it's faster to learn anyway. If you want wrong answers, more professionally presented then anything else is fine.
On a final note, myself and anyone else who has worked on the BIABacus would have much preferred the other software to be excellent. It would have saved us a lot of hours we never wanted nor intended to spend creating some brewing software that not only actually does work but is also a heap more powerful.
I better stop writing
. Tsar, if you do want to persist on the BeerSmith thing then you will have to spend three or four hours at least studying the BeerSmith2 guide that was written on this site and all it's sub-links. Or, you can just fill out your kettle diameter and height in Section B of the BIABacus. Doing the latter will put you on a much faster more educated path than the former.
P.S. I know the above is not what you are hoping for but don't shoot the messenger please!!! I've paid for every brewing software there is over the years so don't you be worried. The BIABacus is, apart from the above, a heap more interesting than any of the others. Get into it!!!