Advanced usage

Used / remaining space

After packing it is possible to see how much physical space in each PackedBox is taken up with items, and how much space was unused (air). This information might be useful to determine whether it would be useful to source alternative/additional sizes of box.

At a high level, the getVolumeUtilisation() method exists which calculates how full the box is as a percentage of volume.

Lower-level methods are also available for examining this data in detail either using getUsed[Width|Length|Depth() (a hypothetical box placed around the items) or getRemaining[Width|Length|Depth() (the difference between the dimensions of the actual box and the hypothetical box).


BoxPacker will always try to pack items into the smallest box available

Example - warning on a massively oversized box


    // assuming packing already took place
    foreach ($packedBoxes as $packedBox) {
        if ($packedBox->getVolumeUtilisation() < 20) {
            // box is 80% air, log a warning

Custom Constraints

For more advanced use cases where greater control over the contents of each box is required (e.g. legal limits on the number of hazardous items per box, or perhaps fragile items requiring an extra-strong outer box) you may implement the BoxPacker\ConstrainedItem interface which contains an additional callback method allowing you to decide whether to allow an item may be packed into a box or not.

As with all other library methods, the objects passed into this callback are your own - you have access to their full range of properties and methods to use when evaluating a constraint, not only those defined by the standard BoxPacker\Item interface.

Example - only allow 2 batteries per box

    use DVDoug\BoxPacker\Box;
    use DVDoug\BoxPacker\Item;
    use DVDoug\BoxPacker\ItemList;

    class LithiumBattery implements ConstrainedItem

         * @param ItemList $alreadyPackedItems
         * @param TestBox  $box
         * @return bool
        public function canBePackedInBox(ItemList $alreadyPackedItems, Box $box)
            $batteriesPacked = 0;
            foreach ($alreadyPackedItems as $packedItem) {
              if ($packedItem instanceof LithiumBattery) {

            if ($batteriesPacked < 2) {
                return true;  // allowed to pack
            } else {
                return false; // 2 batteries already packed, no more allowed in this box