Let W a be an affine Weyl group. In 1987 Jian Yi Shi gave a characterization of the elements w ∈ W a in terms of Φ + -tuples (k(w, α)) α ∈ Φ + called the Shi vectors. Using these coefficients, a formula is provided to compute the standard length of W a . In this note we express the twisted affine length function of W a in terms of the Shi coefficients.