This is a simple calculation, here is an example:
If you have a texture size of 4096 * 4096 pixels and want a texture accuracy of 1 pixel = 1mm, you cover 4096 * 4096 mm2, that is divided by 1000000 (mm2 in m2) = 16.7 m2.
You get the information about the surface from Metashape, you can choose the size and number of textures yourself.
Dieter