I wish to know how big my database using php. How you can display the dimensions in mb entire database? Size in mb a particular request?

Do this to obtain the size in bytes:

mysql_select_db("yourdatabase");  
$q = mysql_query("SHOW TABLE STATUS");  
$size = 0;  
while($row = mysql_fetch_array($q)) {  
    $size += $row["Data_length"] + $row["Index_length"];  
}

then to transform in mb:

$decimals = 2;  
$mbytes = number_format($size/(1024*1024),$decimals);
SELECT table_schema "Data Base Name",
sum( data_length + index_length ) / 1024 /
1024 "Data Base Size in MB",
sum( data_free )/ 1024 / 1024 "Free Space in MB"
FROM information_schema.TABLES
GROUP BY table_schema ;

Try querying information_schema.