/**
 * Display as Columns
 *
 */
function be_portfolio_post_class( $classes ) {

	if ( is_main_query() ) { // conditional to ensure that column classes do not apply to Featured widgets
		$columns = 3; // Set the number of columns here

		$column_classes = array( '', '', 'one-half', 'one-third', 'one-fourth', 'one-fifth', 'one-sixth' );
		$classes[] = $column_classes[$columns];
		global $wp_query;
		if( 0 == $wp_query->current_post || 0 == $wp_query->current_post % $columns )
			$classes[] = 'first';
	}

	return $classes;
}
add_filter( 'post_class', 'be_portfolio_post_class' );