Baker percentages, weights, volumes, and such So a basic bread recipe might look like (off top of head, not sure if these amounts make any sense)

100 Bread Flour
 30 Water
  1 oil
....


I know the flour is in weight ounces, but often times in side-by-side recipes I see the water converted into fluid ounces (8 ounces of water equaling 1c).  I know sometimes it just so happens that they're the same, but with water that is not so.  1 fl oz water ~= 1.05 av oz water.  Close, but off by near 1/2 oz by the time you add 8 of them.

So which do bakers use with fluids?  Do they use av or fl?  Should I expect to be able to weigh my fluids along with everything else or do I need to convert to fl?
If specific units are not given (i.e. you just have a ratio), then you should always go by weight, not volume.

Everything that happens in baking, every chemical reaction, is based on the actual number of molecules of a particular ingredient, which corresponds to its weight.  Volume is simply a rough approximation used in many home cooking/baking recipes.

Note that if using metric measurements (g or mL) then the weight vs. volume measurements actually are the same for water.  So consider using metric for baking, if you can, because that way the conversions are much easier and you can measure out your liquids in a measuring cup without having to do any conversion math.