Dry basis is an expression of a calculation in chemistry, chemical engineering and related subjects, in which the presence of water (H₂O) (and/or other solvents) is neglected for the purposes of the calculation.^[1] 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,^[2] 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.^[3]

Example

An aqueous solution containing 2 g of glucose and 2 g of fructose per 100 g of solution contains 2/100=2% glucose on a wet basis, but 2/4=50% glucose on a dry basis. If the solution had contained 2 g of glucose and 3 g of fructose, it would still have contained 2% glucose on a wet basis, but only 2/5=40% glucose on a dry basis.

Frequently concentrations are calculated to a dry basis using the moisture (water) content :

${\displaystyle {\text{Dry Basis Concentration))={\text{As Is Concentration))\times {\frac {100}{100-{\text{PercentMoisture))))}$

In the example above the glucose concentration is 2% as is and the moisture content is 96%.

${\displaystyle 2\%\times {\frac {100}{100-96))=50\%}$