The size of a zip file in your finder will be different compared to Google or Amazon Drive for a few reasons.
First, the compression of the file could be different. Different file compression algorithms can be used, some of which compress better than others, which explains why the same zip file can appear smaller or larger on different platforms.
Second, the way files are stored can be different. The OS X filesystem can use additional metadata to store information about files, while Google or Amazon Drive may not use that data. That would cause the same file to appear larger on one platform than the other.
Finally, some programs may include hidden files that are not visible to users, but are included in the overall size of the file. This can also make the size of a zip file appear different in Finder compared to other cloud storage platforms.
In conclusion, the size of a zip file in Finder can differ from the size of the same zip file on other cloud storage platforms. This can be due to differences in file compression, metadata, as well as hidden files.