Working without the notion of DPI
You may already be used to the notion of DPI (dots per inch).
The DPI is a pixel density unit often used in imaging and printing software packages. The higher the DPI value of an image, the more pixels it contains and the sharper the printed image will be.
In the animation field, the measurement used is the pixel. The notion of pixels is more practical as it adapts to the specificities of both metric and non-metric systems.
For example : the European PAL format uses a resolution of 720 pixels in width and 576 pixels in height, whereas the American NTSC format uses a resolution of 720 pixels in width and 486 pixels in height.
The global size of your animation in centimeters, meters or inches depends entirely on the TV or cinema screen used to view them.