public function getVolumeUtilisation(): float
    {
        $itemVolume = 0;
        $boxVolume = 0;

        /** @var PackedBox $box */
        foreach ($this as $box) {
            $boxVolume += $box->getInnerVolume();

            /** @var PackedItem $item */
            foreach ($box->getItems() as $item) {
                $itemVolume += ($item->getItem()->getWidth() * $item->getItem()->getLength() * $item->getItem()->getDepth());
            }
        }

        return round($itemVolume / $boxVolume * 100, 1);
    }