Build with the Fits In The Box API
A REST API for 3D bin packing, shipping-tier logic, and packing-aware Shopify experiences. Pack items into the smallest possible boxes, calculate shipping outcomes, and power storefront upsell logic from a single API call.
Quick Start
Three steps to your first pack result.
1. Get your API key
Install the app on Shopify, then go to Settings > API Keys in the Fits In The Box admin. Your key starts with fitb_.
2. Pack items
Send item dimensions and get back the optimal box assignment.
curl -X POST https://api.fitsinthebox.com/v1/pack \
-H "Authorization: Bearer fitb_your_key_here" \
-H "Content-Type: application/json" \
-d '{
"items": [
{
"name": "Blue T-Shirt",
"length": 10.0,
"width": 8.0,
"height": 1.5,
"weight": 0.3,
"quantity": 2
},
{
"name": "Ceramic Mug",
"length": 4.5,
"width": 4.5,
"height": 5.0,
"weight": 0.8,
"quantity": 1
}
],
"dimension_unit": "in",
"weight_unit": "lb"
}'3. Parse the response
The API returns box assignments with utilization and cost.
{
"boxes": [
{
"box_name": "Medium Flat Rate",
"items": ["Blue T-Shirt x2", "Ceramic Mug"],
"utilization": 0.62,
"shipping_cost": 15.05
}
],
"total_shipping_cost": 15.05,
"total_boxes": 1
}Two Pack Modes
Choose the mode that fits your integration.
Raw Dimensions
Send item measurements directly. Works without Shopify — use it from any platform or custom storefront.
POST /v1/pack
{
"items": [
{
"name": "Widget",
"length": 6.0,
"width": 4.0,
"height": 3.0,
"weight": 1.2,
"quantity": 1
}
],
"dimension_unit": "in",
"weight_unit": "lb"
}Shopify Product IDs
Send Shopify variant IDs and the API resolves dimensions from your synced product catalog. Includes upsell suggestions.
POST /v1/pack/shopify
{
"line_items": [
{
"variant_id": 44012345678,
"quantity": 2
},
{
"variant_id": 44087654321,
"quantity": 1
}
]
}Authentication
All API requests require a Bearer token in the Authorization header. Keys are prefixed with fitb_ and can be generated and rotated in the Fits In The Box admin panel under Settings > API Keys.
Authorization: Bearer fitb_your_key_hereRate Limits
Monthly Quota
5,000 requests/month on the free tier. Pro plan includes higher limits.
Burst Limit
100 requests/hour to prevent abuse. Responses include X-RateLimit-Remaining headers.