[Dunny]

just follow the pattern mate, i added one level so you can see

$level = "";
$level1 = '1';
$level2 = '2';
$level3 = '3';
$level4 = '4';
$level5 = '5';
$level6 = '6';
if ($post[posts] > 900 )
{ $level .= $level6; }
elseif ($post[posts] > 800 )
{ $level .= $level5; }
elseif ($post[posts] > 400 )
{ $level .= $level4; }
elseif ($post[posts] > 200 )
{ $level .= $level3; }
elseif ($post[posts] > 100 )
{ $level .= $level3; }
else // ($post[posts] > 0)
{ $level .= $level1; }