Sputtering yields for different ions and materials at low ion energies have a similar energy dependence. Due to this similarity, yield data can be characterized by a normalized energy function and two parameters for each ion target combination. One of these parameters is the threshold energy. An energy scaling can be based on this parameter. The other parameter is a multiplication factor. Both parameters depend mainly on the ion and target massM1andM2and on the surface binding energyEB. An analytic expression for the normalized functions and both the parameters is given. This empirical relation also allows an estimate of unknown sputtering data, ifM1,M2, andEBare noted. A physical interpretation of the empirical relation is given for the caseM1≪M2, as in this case special collision processes which dominate the sputtering can be identified.