Using PHP's filesize() Function to Retrieve and Convert File Sizes

In PHP development, we often need to obtain a file's size, which requires the built‑in function filesize() . The filesize() function returns the size of a file in bytes.

The basic syntax of filesize() is:

filesize(string $filename): int|false

Here $filename is the name of the file whose size you want, which can be a local path or a remote URL. The function returns an integer representing the size in bytes, or false on failure.

Example: suppose we have a file test.txt and we want to get its size.

$filename = 'test.txt';
$size = filesize($filename);

if ($size !== false) {
    echo "文件的大小是：" . $size . " 字节";
} else {
    echo "获取文件大小失败";
}

The code calls filesize() to store the size of test.txt in $size , checks whether $size is not false , and prints the size in bytes if successful; otherwise it prints an error message.

Note that the size returned by filesize() is in bytes. To convert it to other units such as kilobytes, divide by 1024. For example:

$filename = 'test.txt';
$size = filesize($filename);

if ($size !== false) {
    $size_kb = round($size / 1024, 2);
    echo "文件的大小是：" . $size_kb . " KB";
} else {
    echo "获取文件大小失败";
}

In this snippet the file size is divided by 1024 and the round() function is used to keep two decimal places, storing the result in $size_kb , which is then printed with the KB unit.

Summary

The filesize() function is a practical PHP utility for quickly obtaining a file's size; developers can use it to retrieve the size in bytes and, by dividing by 1024 and optionally rounding, convert the value to kilobytes or other units as needed.