iOS has a handy formatter for file sizes. Here is an example of formatting at long into a readable string:
// Get file size
unsigned long long size = [[NSFileManager defaultManager]
attributesOfItemAtPath:path error:nil].fileSize;
NSLog(@"size: %@", @(size));
// Format file size to a readable string
NSString * fileSize = [NSByteCountFormatter stringFromByteCount:size
countStyle:NSByteCountFormatterCountStyleFile];
NSLog(@"fileSize: %@", fileSize);
Output:
size: 65346
fileSize: 65 KB