Custom Tariffs or tariffs nomenclature is a classified system for all goods with international business significance. Tariff nomenclature is organized based on a regular basis by dividing the products to large and small groups that are further subdivided to headings and subheadings, chapters, and sections (e.g. import and export regulations). Custom tariffs are of particular significance for customs purposes, customs clearance, customs statistics, international transport, and knowing and introducing products.
Among different custom tariffs, we can refer to Customs Cooperation Council Nomenclature (CCCN), Brussels Tariff Nomenclature (BTN), Geneva Tariff, and HS. Custom tariffs are international and almost all countries follow a nomenclature. It is worth noting that most of the WOT member countries use HS tariff system.
In terms of being extracted from a custom nomenclature, tariff conditions, rates of customs duty, and other import duties, customs tariffs of countries are not necessarily the same. So, import export terms and conditions may be different based on the countries requirements.
Customs duties and commercial benefits are the sources of custom tariffs and qualitative value of the goods is a criteria and basis for calculating import duties and trading profits.
Methods of calculating import duties are:
1-    Value-based method: tariff rate multiplying by custom value of goods equals to custom duty.
2-    Defined and special method: custom duties are defined based on quantity of goods and there is a predefined price for each units of goods which is not related to the goods custom value.
3-    Combined method: quantity and custom value of goods are both considered in this method. For some goods, such as Chinese, import duties are 90% or 120000 IRR*Kg; whichever is more has to considered.
Given the following reasons, the value-based method is of higher priority:
1-    It is more fair. Goods with higher prices have more import duties that goods with lower prices.
2-    Negotiations and agreements becomes easier because the method is simple.
3-    Generally, countries use this method.