Regex match space or nothing

I'm trying to match the following:

4acres
4 acres
44 acres

but it only works if there is a space at the moment:

preg_match("/([0-9]+)\sacres/i", $row[5], $found);

PHP:

I tried the following but no luck ..

preg_match("/([0-9]+)([\s|])acres/i", $row[5], $found);

PHP:

 

Try following

preg_match_all('/\d*\s*acres/i', $row[5], $found);

Code (markup):

 

try this..

preg_match("/[0-9]+[ ]?acres/i", $row[5], $found);

PHP: