The cost of equity is essentially the return that the investors require in order to invest in a company. In other words, what is the minimum return they are seeking for the risk that a business has. There are a lot of methods to calculate the cost of equity. A common method is to use the dividend growth model where the cost of equity is :
Ke=((Dividend*(1+growth rate of dividends))/Market Value of a share))+ growth rate of dividends
You can also use the CAPM (capital asset pricing model) to calculate the cost of equity.