I managed to solve it and am posting for future readers. The issue was that I was focusing on the wrong variable. I was trying to loop through the subfield value but it was already being looped and calculated to a different variable.
<?php
if( have_rows('packaging_sessions') ): ?>
<table>
<caption>Packaging Sessions
</caption>
<thead>
<tr>
<th>Quantity × Capacity
</th>
<th>Volume
</th>
</tr>
</thead>
<tbody>
<?php
$total_finished_packages = 0;
while( have_rows('packaging_sessions') ): the_row();
// vars
$packaging_capacity = get_sub_field('packaging_capacity'); // The select subfield in the repeater (size)
$package_capacity_value = esc_attr($packaging_capacity['value']); // The select field's values
$package_capacity_label = esc_html($packaging_capacity['label']); // The select field's labels
$packaging_quantity = get_sub_field('packaging_quantity'); // The quantity of packaged units
$finished_package = $packaging_quantity * ($package_capacity_value * .001); // The quantity x size
?>
<tr>
<td><!-- Quantity & Capacity -->
<?php echo (int)$packaging_quantity . " × " . $package_capacity_label ?>
</td>
<td><!-- Volume -->
<?php echo $finished_package; ?>
</td>
</tr>
<?php
// Iterate through the capacities and quantities
$total_finished_packages += $packaging_capacity * $packaging_quantity ;
?>
<?php endwhile; ?>
</tbody>
</table>
<!-- Sum volume of all package combinations -->
<?php echo 'Total packaged volume is ' . $total_finished_packages ; ?>
Brilliant, John. Thank you for pointing me in the right direction!
