wc-area-instead-quantity.php

<?php

/**
 * Change min qty to area
 */
function ywp_set_min_qty_decimal( $val ) {
    return 0.1;
}

add_filter('woocommerce_quantity_input_min', 'ywp_set_min_qty_decimal');

/**
 * Change qty steps
 */
function ywp_change_qty_steps_to_decimal( $val ) {
    return 0.1;
}

add_filter('woocommerce_quantity_input_step', 'ywp_change_qty_steps_to_decimal');

/**
 * Removes wc qty validation
 */
remove_filter( 'woocommerce_stock_amount', 'intval' );

/**
 * Add wc qty float validation
 */
add_filter( 'woocommerce_stock_amount', 'floatval' );

/**
 * Add js to product
 */
function ywp_update_product_price_on_qty_change() {
	  global $product;
  
	  echo '<div id="product-price" style="display:inline-block">قابل پرداخت: <span></span></div>';
  
	  $price    = $product->get_price();
	  $currency = get_woocommerce_currency_symbol();
  
	  wc_enqueue_js( "		
		    jQuery('[name=quantity]').on('input change', function() { 
			      let qty = $(this).val();
			      let price = '" . esc_js( $price ) . "';
			      let price_string = (price*qty).toFixed(2);
			      jQuery('#product-price > span').html(price_string+' '+" . esc_js( $currency ) . ");
		     }).change();
	  " );
}

add_action( 'woocommerce_after_add_to_cart_button', 'ywp_update_product_price_on_qty_change' );