src/Model/Modifiers/Shipping/Weight.php
public function Weight()
    {
        if ($this->weight) {
            return $this->weight;
        }
        $weight = 0;
        $order = $this->Order();
        if ($order && $orderItems = $order->Items()) {
            foreach ($orderItems as $orderItem) {
                if ($product = $orderItem->Product()) {
                    $weight = $weight + ($product->Weight * $orderItem->Quantity);
                }
            }
        }
        return $this->weight = $weight;
    }
public function Weight()
    {
        if ($this->weight) {
            return $this->weight;
        }
        $weight = 0;
        $order = $this->Order();
        if ($order && $orderItems = $order->Items()) {
            foreach ($orderItems as $orderItem) {
                if ($product = $orderItem->Product()) {
                    $weight = $weight + ($product->Weight * $orderItem->Quantity);
                }
            }
        }
        return $this->weight = $weight;
    }
Calculate the total weight of the order

@return number