Calculate offline map download size for a square km for each zoom level?

I am working on estimation of how much will I have to download to make maps available offine at different zoom levels. What I am looking for is something like below.

zoomLevel,sizeInKM,downloadInGB
1,1,0.065
2,1,0.5

I have read different articles from OpenStreetMaps, Google Maps API and Bing Maps. References below, none of them talk about how to relate size to kilometers.

What ratio scales do Google Maps zoom levels correspond to?

https://docs.microsoft.com/en-us/bingmaps/articles/bing-maps-tile-system

https://wiki.openstreetmap.org/wiki/Zoom_levels

https://stackoverflow.com/questions/3238611/how-can-i-get-tile-count-tile-x-tile-y-details-without-specifying-zoom-level

If someone has experience with maps, can you show me a direction to get some download size estimates for 1 km square block on a map at different zoom levels for offline viewing.