Capital requirements are designed to ensure that banks will have sufficient capital to repay the depositors and debtors. A bank's “capital” is the difference between the total value of the bank's assets and its total deposits plus debt. That is, the bank's capital is the money that would be left over if the bank were able to liquidate all of its assets to pay off all of its depositors and debtors. If a bank holds a high percentage of “risky” assets (such as loans that could be defaulted on), capital requirements are higher to ensure that the bank will remain solvent—even if some of its loans are not repaid.
Thus the capital requirement does not specify any set requirement for all banks but rather determines the amount of capital that is appropriate to balance the amount of risk a bank carries with its asset allocation.