With the advent of fluorescent whitening agents, the general idea of whiteness has changes. Numerous whiteness formulas by which we evaluate whiteness of white materials have been proposed, but these formulas (including the CIE whiteness formula) were found not to correlate well to visual estimation. In this article, a modified CIE whiteness formula dealing with the tint and the excitation purity is proposed. There is a significant correlation between this formula and the visual estimation of whiteness.