Mass fraction (chemistry)

In chemistry, the mass fraction of a substance within a mixture is the ratio w i {\displaystyle w_{i}} (alternatively denoted Y i {\displaystyle Y_{i}} ) of the mass m i {\displaystyle m_{i}} of that substance to the total mass m tot {\displaystyle m_{\text{tot}}} of the mixture. Expressed as a formula, the mass fraction is: w i = m i m tot .