To fill a lack in sputtering yield data for a B 4C material which may be a promising plasma-facing material in fusion devices, the yields of H +, D +, T +, He +, B +, C +, Ne +, Ar + and Kr + ions were calculated for this multi-component material for normal incidence with a computer simulation code ACAT. A fitting formula of sputtering yield for a B 4C was proposed based on an empirical formula for monoatomic target materials at normal incidence. By fitting the formula to the calculated data, best-fit values of the parameters included in it were derived for the material. Good agreement was found between the formula and the data. Thus, the formula proposed for the multi-component material provides a way to estimate the erosion of a B 4C material irradiated with above ions at normal incidence. Preferential sputtering for this material was also mentioned briefly.