We present a volume-explicit equation of state for hard spheres and their mixtures that performs well in the isotropic, metastable, and random close-packed regions. The equation gives the exact second and third virial coefficients at low pressures and predicts the correct random close- packed density at infinite pressures. Comparison with simulation data showed that the equation is accurate for the isotropic, metastable, and random close- packed regions. The equation predicts phase splitting in the metastable region for molecules with large size differences.