If the concentrations of weak acid and salt of its conjugate base in a buffer are a and b, respectively. The buffer capacity of the solution will be

The buffer capacity is $2.303\frac{\left[\text{ base }\right]\left[\text{ acid }\right]}{\left[\text{ base }\right]+\left[\text{ acid }\right]}=2.303\left(\frac{ba}{b+a}\right)$

Buffer capacity is the maximum quantity of acid or base that can be added to a volume of a buffer solution without appreciably changing the pH.