In PHP, you can get the file size in bytes using the filesize() function. The filesize() function returns the size of a file in bytes. Here's an example of how to use it:
$file = 'path/to/your/file.ext';
$fileSize = filesize($file);
echo $fileSize . " bytes";
In the above example, replace 'path/to/your/file.ext' with the actual path to your file. The filesize() function will return the size of the file in bytes, which you can then use as needed.