How do I pre-estimate the size of a file?

Question

symfony

How can you pre-estimate the size of a generated file using dumpFile of the Symfony\Component\Filesystem class ?
In the class itself, I did not notice such an option.
Or do you still have to create a temporary file and see how long it took?

The code:

use Symfony\Component\Filesystem\Filesystem;

$filesystem = new Filesystem();

$filesystem->touch($_SERVER['DOCUMENT_ROOT'] . $url);

$filesystem->dumpFile($_SERVER['DOCUMENT_ROOT'] . $url, $data);    // 5797960 bytes

strlen($data);        // 5236968 bytes