WordPress | ACF | Adaptive Repeater

acf_repeater_flexible.php

<style>
ul {margin:0; padding:0; list-style:none; overflow:auto}
ul li {float:left}
ul.half li {width:50%}
ul.thirds li {width:calc(100% / 3); width:33.33%}
ul.quarters li {width:25%}
</style>
<?php
if( have_rows('repeater_field_name') ): 
    $repeater = get_field('repeater_field_name');
	$count = count( $repeater );
	echo '<ul class="';
	if ( $count <= 2 || $count == 4 ) {
		echo 'half';
	} elseif ( $count == 3 || $count == 5 || $count == 6 || $count == 9 ) {
		echo 'thirds';
	} else {
		echo 'quarters';
	}
	echo '">';
	while( have_rows('repeater_field_name') ): the_row(); 
		$title = get_sub_field('title');
		echo '<li>';
		echo '<h3>' . $title . '</h3>';
		echo '</li>';
	 endwhile; 
	 echo '</ul>';
endif;
?>

ACF Repeater with content dependent list item widths

By counting the number of repeater rows we can ensure the list items fit the space available.