Dry basis is an expression of a calculation in chemistry, chemical engineering and related subjects, in which the presence of water (HO) (and/or other solvents) is neglected for the purposes of the calculation. Water (and/or other solvents) is neglected because addition and removal of water (and/or other solvents) are common processing steps, and also happen naturally through evaporation and condensation; it is frequently useful to express compositions on a dry basis to remove these effects.
In food science and pharmacy, dry basis also refers to a ratio of the weight of water to the weight of a completely dry material, as opposed to the wet basis ratio of water to a material under normal conditions that contains a measurable amount of moisture.