The amount of liquid, usually in the form of water, that is contained within a substance. The relationship is expressed either on a dry basis as the amount of water per unit mass of substance, or on a wet basis as the amount of water per unit mass of substance with water. Both are expressed as a percentage for which the relation between the two is:

where x_d is the moisture content on a dry basis and x_w is the moisture content on a wet basis. The moisture content measured on a wet basis can exceed 100 per cent.