Ok, found, the code is:
global $product;
$price = $product->get_price();
$weight = $product->get_weight();
$id = $product->get_id();
$value = number_format( 1000 * $price / $weight, 2 );
update_field(‘price_per_kilo’, $value, $id); // this code updates data for this field
the_field(‘price_per_kilo’, $product->$id ); //show price per kilo
