WC_Cart::get_product_subtotal PHP Method

    public function get_product_subtotal($product, $quantity)
    {
        $price = $product->get_price();
        $taxable = $product->is_taxable();
        // Taxable
        if ($taxable) {
            if ('excl' === $this->tax_display_cart) {
                $row_price = wc_get_price_excluding_tax($product, array('qty' => $quantity));
                $product_subtotal = wc_price($row_price);
                if ($this->prices_include_tax && $this->tax_total > 0) {
                    $product_subtotal .= ' <small class="tax_label">' . WC()->countries->ex_tax_or_vat() . '</small>';
                }
            } else {
                $row_price = wc_get_price_including_tax($product, array('qty' => $quantity));
                $product_subtotal = wc_price($row_price);
                if (!$this->prices_include_tax && $this->tax_total > 0) {
                    $product_subtotal .= ' <small class="tax_label">' . WC()->countries->inc_tax_or_vat() . '</small>';
                }
            }
            // Non-taxable
        } else {
            $row_price = $price * $quantity;
            $product_subtotal = wc_price($row_price);
        }
        return apply_filters('woocommerce_cart_product_subtotal', $product_subtotal, $product, $quantity, $this);
    }