Measurements of the ratios of charged kaon decay rates for Ke3/K2pi, Kmu3/K2pi and Kmu3/Ke3 are presented. These measurements are based on charged kaon decays collected in a dedicated run in 2003 by the NA48/2 experiment at CERN. The results obtained are Ke3/K2pi = 0.2470 +- 0.0009 (stat) +- 0.0004 (syst)...