Calculating tariffs is a complex process, and there's no single "simple" formula. It involves economic, political, and strategic considerations. However, I can outline some of the key factors and approaches used:

Key Factors:

Trade Deficits:
One approach focuses on addressing trade imbalances. Some calculations aim to determine tariff rates that would bring bilateral trade deficits closer to zero. This involves analyzing import and export data.
Reciprocity:
Another method involves matching the tariffs imposed by other countries on U.S. goods. The idea is to create a level playing field. This requires comparing tariff rates across different nations.
Industry Protection:
Tariffs can be used to protect domestic industries from foreign competition. This involves assessing the impact of imports on specific sectors and setting tariffs to safeguard those industries.
National Security:
In some cases, tariffs are imposed for national security reasons, such as protecting critical industries or technologies.
Political Considerations:
Trade policy is often influenced by political factors, including domestic pressures and international relations.
General Concepts:

Harmonized Tariff Schedule (HTS):
The U.S. uses the HTS to classify imported goods and determine applicable tariff rates. This system assigns specific codes to products, which correspond to different tariff levels.
Trade Agreements:
Trade agreements, such as those with the World Trade Organization (WTO) or bilateral agreements, can significantly impact tariff rates. These agreements often establish rules and limits on tariffs.
Economic Impact:
Calculating tariffs also involves assessing their potential economic impact, including effects on consumer prices, domestic production, and international trade flows.
Where to find more detailed information:

United States Trade Representative (USTR):
The USTR is responsible for developing and coordinating U.S. trade policy. Their website provides information on trade agreements, tariff rates, and other trade-related issues.
U.S. Customs and Border Protection (CBP):
CBP enforces customs laws and regulations, including the collection of tariffs. Their website offers resources on importing goods into the U.S.
It is important to remember that tariff calculations are often very complex, and are subject to change based on many different factors.