I looked at various implementations of Material Design and it seems that they all have height: 64px and I am wondering why ? What is the calculation based on ? Why not 65px or 50px ?
However, the App Bar in Material Design is not actually always 64px.
According to Material Design Guidelines:
All components align to an 8dp square baseline grid for mobile, tablet, and desktop. Iconography in toolbars align to a 4dp square baseline grid.