Leverage is the ability to gear your account into a position greater than your total account margin. For instance, if a trader has $1,000 of margin in his account and he opens a $100,000 position, he leverages his account by 100 times, or 100:1. If he opens a $200,000 position with $1,000 of margin in his account, his leverage is 200 times, or 200:1. Increasing your leverage magnifies both gains and losses.
To calculate the leverage used, divide the total value of your open positions by the total margin balance in your account. For example, if you have $10,000 of margin in your account and you open one standard lot of USD/JPY (100,000 units of the base currency) for $100,000, your leverage ratio is 10:1 ($100,000 / $10,000). If you open one standard lot of EUR/USD for $150,000 (100,000 x EURUSD 1.5000) your leverage ratio is 15:1 ($150,000 / $10,000).