Lebesgue Constants are two set of constants in mathematical field. One is related to the approximation of functions in Fourier Series other is relates to the computation of Lagrange interpolating polynomials. The constant determines how best the given function is by comparing the best degree of the polynomials. The constant is named after Henri Lebesgue. The value of the constant is equal to 1.64218 84352 22121 13687 denoted by L2. Lebesgue constant is also referred to as Lebesgue number.