BuddyPress.org

You’ll need some custom sql. Put this in bp-custom.php

function contributor_count() { 
  global $wpdb;
		
  $contributor_count = $wpdb->get_var( "SELECT COUNT(user_id) FROM {$wpdb->prefix}usermeta WHERE meta_key = '{$wpdb->prefix}capabilities' AND meta_value LIKE '%contributor%'" );
	
  return $contributor_count; 
}

Use it wherever you want like this:

echo contributor_count();

@dta_madrid

Further to @shanebp’s method, WordPress has a function called count_users() which can be used to get the number of users in each role.

https://codex.wordpress.org/Function_Reference/count_users

$users = count_users();

// display total users (if you want to).
echo $users['total_users'] . ' total users';

// display count for contributors. 
foreach( $users['avail_roles'] as $role => $count ) {
    if ( $role == 'contributor' )
        echo $count . ' contributors';
}