I have been using the calculator. Good work, I love it.
I have noticed some quirks.
A bit of research on honey (
http://www.fao.org/docrep/w0076e/w0076e04.htm) and it seems to be closer to 11.8#s per US Gallon.
Also, I noticed that the assumption of 12#s per gallon applied to maple syrup. Maple syrup with a specific gravity of 1.37 will be closer to 11.41#s per US Gallon.
something that has been confusing me is that if you choose say, Honey and set it to 1 gallon of honey, then select litres instead of a direct conversion it comes to 7.258 liters. 1 US Gal being of course, 3.785 L.
It doesn't seem to be a direct doubling of the correct value (it would be 7.570 L).
I actually notice that the assumption that 12#s = 1 gallon is consistent for all materials. For fermentables which you don't have a quoted value for, I would use a table of specific gravities to convert weight (say #s to kilos) to volume (liters to gallons). So, say, I ask for 7#s of blueberries and then ask it to convert to gallon. It would take the 7#s, convert to 3.17 kg, then look up the sugar content of blueberries. It can be as high as 15% when ripe. So we'll go with 15% sugar. The specific gravity of sugar water with 15% sugar is say... 1.07. 3.17 kg / 1.07 = 2.96 liters.
This is 0.78 gallons.
btw, the reason I just posted all that dribble is because I'm calculating some stuff for my blueberry mead...
So anyhow, I would suggest fixing at least the gallons to liters conversion (and any other conversions that are screwy... like 1 us gallon to 245.436 fl oz).
The calculator is great otherwise though.