$args = array(
'posts_per_page' => 5,
'cat' => $current_category->term_id,
'meta_query' => [
'relation' => 'AND',
[
'key' => 'size',
'value' => 50,
'compare' => '>'
],
[
'key' => 'size',
'value' => 100,
'compare' => '<=',
]
]
);
$query = new WP_Query($args);
'key' => 'size,
'value' => array(50, 100 ),
'type' => 'NUMERIC',
'compare' => 'BETWEEN'