Required margin is the amount your broker sets aside to keep a leveraged position open. It equals the position value divided by the leverage.
How the calculation works
One lot of EUR/USD at 1.1000 is worth 110,000 US dollars. At 30:1 leverage the margin is about 3,667 dollars. Margin is not the amount at risk: the position can lose more or less than the margin, depending on how far the price moves.