IEC separately defines the negative sequence and zero sequence three phase unbalanced ratio. So, the definition is not unique. The unbalanced ratio calculated by measured RMS values has no correspondence with the sequence component definition. It makes for confusion in actual engineering. Based on the size relationship between RMS of the sequence component and phasor, it is proposed to measure the three-phase balance ratio using the square of the three-phase positive sequence component RMS divided by the square of the phasor RMS. In this way the definition is unified no matter whether it is with or without the zero sequence component. On this basis, the method of using measurement values to get sequence components is constructed, aiming at both the line voltage and current without the zero sequence component and phase voltage and current with the zero-sequence component. The measurement RMS unbalanced ratio definition has correspondence with the sequence component. The examples show that the proposed method of sequence component measurement is more suitable for a three-phase three-wire system and a three-phase four-wire system. The definition based on measured values corresponds with the sequence component definition. It guarantees the uniqueness of the three-phase unbalanced ratio in engineering. This work is supported by National Natural Science Foundation of China (No. 51607083), Major Natural Science Research Projects of Jiangsu Province University (No. 17KJA470003), and Project of State Key Laboratory of Smart Grid Protection and Control.