> ## Documentation Index
> Fetch the complete documentation index at: https://shipmagic-docs.speedysquirrelhq.com/llms.txt
> Use this file to discover all available pages before exploring further.
# How to Setup Packing Algorithm for your Products
> Configure boxes and packing distribution so carrier rates reflect real parcels
When ShipMagic asks a carrier for a rate, the carrier needs to know what it's quoting for. The packing algorithm decides how your cart's items are distributed into parcels before that question is asked.
Get this right and live rates match what you're actually charged. Get it wrong and every quote is off.
## Packaging box distribution
Every live carrier rate has a **Packaging box distribution** setting with four options:
| Option | How items are packed |
| - | - |
| **None - Use product dimensions** | Each product is quoted using its own dimensions. No boxes involved. |
| **By items count** | Items are packed into your boxes up to a maximum number of items per box. |
| **By items volume** | Items are packed by volume using a 3D bin-packing algorithm. |
All options except **None** need you to define at least one box. **By items volume** additionally needs accurate **product dimensions** — see [Adding Dimensions to Products](/adding-dimensions-to-products). Without them the algorithm has nothing to pack.
## Defining boxes
Once you pick a distribution method other than **None**, a box table appears. Each box takes:
| Field | Meaning |
| - | - |
| **Max limit** | For *By items count*: how many items fit in this box. For *By weight*: the weight ceiling. |
| **Length / Width / Height** | The box's internal dimensions, in millimetres. |
| **Weight** | The weight of the **empty box**, added to the parcel's total. |
Add as many box types as you use with **Add another box**.
Include the empty box weight. It's easy to leave at zero, but a heavy carton on a light order can shift the parcel into the next weight bracket and make every quote too low.
## How the 3D algorithm works
**By items volume** is the most sophisticated option. It uses 3D bin packing: each item is treated as a rectangular solid with a width, height, depth, and weight, and the algorithm fills your boxes by volume, tracking remaining space and accumulated weight as it goes.
When one box is full it opens another of the same or the next suitable type, until every item is placed. ShipMagic then asks the carrier for a rate on the resulting set of parcels.
The algorithm packs by **volume**, not by simulating physical orientation. It won't detect that a long item cannot fit diagonally into a box whose volume is technically sufficient. For awkward-shaped goods, define a box that genuinely fits them and use **By items count**.
## Choosing a method
**None - Use product dimensions** suits stores where each product ships in its own packaging — furniture, appliances, anything already boxed by the manufacturer.
**By items count** is the simplest to reason about and the easiest to keep accurate. If you ship a fairly uniform catalogue in one or two carton sizes, start here.
**By weight** suits dense goods where weight, not space, is the binding constraint.
**By items volume** is the most accurate for mixed carts of varied sizes, and the most demanding — every product needs correct dimensions.
Start with **By items count** and move to **By items volume** once your dimension data is complete and trustworthy. An accurate simple model beats an inaccurate sophisticated one.
## Pallets
For freight-scale orders, ShipMagic also supports pallet configuration — see the pallet fields on carriers that support them, such as Direct Freight Express.
## Verifying your setup
Live carrier rates are hard to eyeball. Test with real carts:
1. Add a cart you know the true shipping cost for
2. Check the rate at checkout against what the carrier actually charges you
3. Try a cart that should need two boxes, and confirm the rate rises appropriately
Always set a **Default rate** on live carrier rates. If the carrier doesn't respond, that fallback is the only thing standing between your customer and a checkout with no shipping options.
## Related
Populate length, width, and height across your catalogue.
Connect a USPS account.
Connect a FedEx account.
When a carrier rate fails to appear.
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