I am not sure if there is a way to directly calculate if there is a step to calculate meters per pixels. You can ensure that if you know the size of the map in pixels and the zoom level, I'm not sure that my calculations are correct, but at 45 degrees latitude (north) the scale is 0.88 meters per pixel at a zoom level of 20, and then this the block doubles with the zoom level ... (for example, with a scale of level 19 it is 0.88 * 2, with 18..0.88 * 4..etc)
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