Km (Michaelis Menten Constant) is the substrate concentration at which the chemical reaction attains half of its maximum velocity. With the increase in concentration of substrate, the enzymatic velocity also increases. At a certain value all the active site of the enzyme molecules are saturated. Increase in substrate concentration does not increase the velocity of the enzymatic reaction. Higher is the affinity of an enzyme for a substrate, lower is the Km value. Km value lies in between ${10}^{-1}$ to ${10}^{-6}\mathrm{M}$ . Km value is independent of enzyme and substrate concentration.