Where is file size stored in an APFS volume?

I can read an APFS container and volume and find the inode for a file successfully but I cannot find the size of a file, in bytes, anywhere in the "Apple File System Reference" documentation, 2020-06-22 version. The best I can see is the number of 4K blocks the file has in it's extents list.

Can anyone point me in the right direction.

Thanks