Nick Wallingford has a very useful page of calculators on his site.
For the one you are looking for, you need to know the volume of syrup
or the weight of the sugar.  From this it looks like the bees would store
about 9 pounds of honey from 20 pounds of sugar at 2:1
Here is the url:

http://www.beekeeping.co.nz/convert.htm#sugarstore2

Ian Watson

> >Suppose I feed my bees say 20lbs of sugar syrup, what weight of
consumable
> >stores end up in the combs as the result of such feeding?.
>
> I should have added that the syrup is 2:1 ie 2 kilos of sugar to 1 litre
(1
> kilo) of water.