Custom Calculation: Apply Non-Standard Shipping Calculations
Overview
With the Custom Calculation feature you may set up non-standard shipping calculations that go beyond standard per-item or per-order logic. It works by defining a custom item — a virtual unit derived from a product attribute — and then charging a fixed rate per each custom item using the FPCI (Fixed Per Custom Item) algorithm in Table Rates or Shipping Rules.
Popular scenarios
- Shipping rate per every "10 items"
- Shipping rate per every "10 lbs"
- Surcharge per every 5 specific items
Shipping Segment must be configured before setting up Custom Calculation — it defines which products the calculation applies to.Custom Calculation: Configuration Steps
Before you start: Create a Shipping Segment for the products this calculation should apply to (e.g. "Toys", "Heavy Items").
- Complete Custom Calculation settings — define algorithm, attribute, value and segment
- Use FPCI (Fixed Per Custom Item) in Table Rates method or Shipping Rule — set the rate per custom item
- Optionally: add Cart Custom Item Quantity condition — for tiered pricing by custom item count
After you finish: test the rate at checkout or with our Test Your Rates tool and check the Activity Feed.
Step 1: Complete Custom Calculation Settings
Step 2: Use FPCI in Table Rates Method or Shipping Rule
In the Table Rates method's Rate settings, select FPCI — Fixed Per Custom Item as the calculation algorithm and enter the cost per custom item in the Value field.
Step 3: Add Cart Custom Item Quantity Condition (optional)
In the Rate's Cart Conditions panel, a dedicated Custom Calculation section lets you restrict the rate to a range of custom item counts. This enables tiered pricing by order size.
Use this condition to set up tiered rates: e.g. $12.00/custom item for 1–2 custom items, $10.00 for 3–5, $8.50 for 6+. Each tier is a separate rate row with its own FPCI value and quantity range.
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