There are different ways of classifying tariffs or customs duties. Using the levy criterion, tariffs may be classified into: (i) specific duties, (ii) ad valorem duties, (iii) combined specific and ad valorem duties, and (iv) sliding scale duties.
Specific duties are flat levies per physical unit (metre, kilo, ton, etc.) of the commodity imported.
Ad valorem duties are, on the other hand, levied as fixed percentage of the value of the imported commodity.
Combined specific and ad valorem duties, when imposed, specify that one or the other, usually whichever, involves lower charge, is payable at the customs.
Sliding scale duties are those which tend to vary with the price of the commodity imported. These may be either specific or ad valorem. Specific sliding scale duties are, however, common in practice.
Another important classification of tariffs is based on the purpose they serve. Using the objective criterion, tariffs are distinguished as: (i) Revenue Duties, and (ii) Protective Duties.
Revenue tariffs are those whose primary purpose is to provide revenue to the State. These are generally at a lower rate and not intended to exclude imports. They are usually levied on imports of consumption goods.
Protective tariffs, on the other hand, are designed to curtail imports of certain goods to protect domestic production.