<?php   $dbname = “databasename”;   ?>

<?php
        mysql_select_db( $dbname );
        $result = mysql_query( “SHOW TABLE STATUS” );
        $dbsize = 0;
        while( $row = mysql_fetch_array( $result ) ) {  
                   $dbsize += $row[ "Data_length" ] + $row[ "Index_length" ];
        }
?>

function formatRawSize($bytes) {
    if(!empty($bytes)) {
        $s = array('bytes', 'kb', 'MB', 'GB', 'TB', 'PB');
        $e = floor(log($bytes)/log(1024));
        $output = sprintf('%.2f '.$s[$e], ($bytes/pow(1024, floor($e))));
        return $output;
    }
}

<?php
        echo “<p>Размер БД ” . formatRawSize( $dbsize ) . “</p>”;
?>