Bank capital is the difference between a bank's assets and its liabilities, and it represents the net worth of the bank or its equity value to investors. Bank capital is one of the most important factors when evaluating a bank's financial health and stability. It serves as an important measure of the bank's ability to absorb losses and maintain operations when faced with financial shocks and can be used to determine the amount of risk that a bank is willing to take on.

Basel I, Basel II, and Basel III standards specify the minimum amount of regulatory bank capital that market and banking regulators closely monitor. Banks must maintain these required levels of capital in order to operate. The first tier measures the bank's financial health and is called Tier 1 capital. Generally, Tier 1 capital consists of shareholders' equity, retained earnings, and other financial instruments that are highly liquid and considered of high credit quality.

Creditors also consider bank capital when assessing a bank's stability. Bank capital is a measure of the amount of money creditors can count on if the bank enters bankruptcy and liquidates its assets. By measuring the capital, creditors can assess the risk of the bank not being able to pay them back if the worst were to happen.

In sum, bank capital is an important measure of a bank's financial health and stability. Banks must maintain required levels of bank capital to meet requirements established by regulatory authorities, while creditors need to know the bank's solvency and creditworthiness to decide how much risk they are willing to take on.