Source

File: wp-includes/media.php

function wp_max_upload_size() {
	$u_bytes = wp_convert_hr_to_bytes( ini_get( 'upload_max_filesize' ) );
	$p_bytes = wp_convert_hr_to_bytes( ini_get( 'post_max_size' ) );

	/**
	 * Filters the maximum upload size allowed in php.ini.
	 *
	 * @since 2.5.0
	 *
	 * @param int $size    Max upload size limit in bytes.
	 * @param int $u_bytes Maximum upload filesize in bytes.
	 * @param int $p_bytes Maximum size of POST data in bytes.
	 */
	return apply_filters( 'upload_size_limit', min( $u_bytes, $p_bytes ), $u_bytes, $p_bytes );
}