You can find that in there site .
 (Initial Margin: The percentage your Net Value is of the total value you can borrow. For example, if you want to borrow 3 BTC and your Initial Margin is 40%, you need to have at least 40% of 3 BTC — or 1.2 BTC — worth of funds in your margin account, less unrealized losses and lending fees. )
You just need to read more . Also i do not recommend you to margin trading without fully understand and read every thing about it . you will prob lose all your money if you not have good knowledge .