Forex trading is attractive because of margin trading. When Forex traders use margin, they are borrowing from their brokers. Margin is a function of your lot size, the leverage ratio you use, and the size of your account. Calculating margin (margin calculator) is relevant to determine if you meet the requirements of your broker to open a position for you.
A Forex calculator can easily calculate your margin, allowing you to know if your broker can guarantee it.
Then, you will know if you have to adjust your lot size or leverage or both. Consequently, position size, leverage ratio, and account currency are important parameters for calculating the required margin.
For forex, the calculation works as follows:
Required Margin = Trade Size / Leverage * account currency exchange rate (if different from the base currency of the pair traded)