It is known that for P n , the subspace of C([−1, 1]) of all polynomials of degree at most n, the least basis condition number ∞ (P n ) (also called the Banach-Mazur distance between P n and n+1 ∞ ) is bounded from below by the projection constant of P n in C([−1, 1]). We show that ∞ (P n ) is in fact the generalized interpolating projection constant of P n in C([−1, 1]), and is consequently bounded from above by the interpolating projection constant of P n in C([−1, 1]). Hence the condition number of the Lagrange basis (say, at the Chebyshev extrema), which coincides with the norm of the corresponding interpolating projection and thus grows like O(ln n), is of optimal order, and for n = 2, 1.2201 . . . ∞ (P 2 ) 1.25.We prove that there is a basis u of P 2 such thatThis result means that no Lagrange basis of P 2 is best conditioned. It also seems likely that the previous value is actually the least basis condition number of P 2 , which therefore would not equal the projection constant of P 2 in C([−1, 1]). As for trigonometric polynomials of degree at most 1, we present numerical evidence that the Lagrange bases at equidistant points are best conditioned.