Wholesale suppliers, food and beverage stores, and any merchant who sells in standardised pack sizes face the same Shopify problem: a customer can add 7 units when the only valid quantities are 6 or 12. Shopify does not natively enforce case-pack or multiple-based buying.
This guide covers how to force case-pack quantities on Shopify using Fold, so customers can only check out with valid pack sizes.
What Are Case Packs and Quantity Multiples?
A case pack is a fixed quantity grouping — a box of 6 cans, a tray of 12 jars, a pallet row of 24 bottles. Quantity multiples enforce that purchases happen in increments: 6, 12, 18, 24 — never 7 or 11.
Common use cases:
- Food and beverage — sold by case or tray, never as single units
- Wholesale B2B — minimum case quantity for cost-effective fulfilment
- Manufacturing supply — components sold in standard run quantities
- Subscription boxes — bundles structured around fixed unit counts
How Shopify Handles Quantities by Default
Shopify’s product settings let you set a stock level and a price. There is no native ‘sell in multiples of X’ field. A customer can enter any quantity they like into the cart — 1, 3, 7, 100. Nothing validates at checkout that the quantity is a valid pack size.
Setting Case Pack Rules with Fold
Step 1 — Install Fold
Fold uses Shopify Functions to validate quantities at checkout. Install it from the Shopify App Store — no theme edits required.
Step 2 — Create a Quantity Increment rule
Open Fold and click Create Rule. Select Quantity Increment (or Sell in Multiples). Choose your target: a specific product, collection, or tag.
Step 3 — Set the increment
Enter your case size — for example, 6. Customers can add 6, 12, 18, 24 — any multiple of 6. If they add 7 or 13, the rule blocks checkout and shows your error message: “This product must be purchased in multiples of 6.”
Step 4 — Combine with a minimum
You can pair a quantity increment with a minimum order quantity. Minimum 6, increment 6 means the smallest valid order is one case. See also: how to set minimum order quantity on Shopify.
Different Rules for Different Products
Create separate rules for each product or collection with its own pack size. Your 330ml cans sell in 6s, your 500ml bottles in 12s, your 1L cartons in 4s. Fold evaluates all active rules at checkout simultaneously. More on targeting by collection: Shopify collection quantity rules.
Wholesale vs Retail Case Sizes
Use customer tag conditions to apply different pack sizes for retail and wholesale. Retail customers buy in 6s; wholesale customers buy in 24s or 48s. This is the same approach as running wholesale and retail from one store.
Frequently Asked Questions
Does the increment rule work on all Shopify plans?
Yes. Fold uses Shopify Functions, available on Basic, Shopify, and Advanced plans. No Shopify Plus required.
What error message does the customer see?
You write the message yourself in Fold’s rule editor. Make it specific: “Please add a multiple of 6 for this product (e.g. 6, 12, 18).”
Can I enforce increments and a minimum at the same time?
Yes. Set a minimum of 6 and an increment of 6. Fold validates both conditions at checkout.
Install Fold to sell in case packs and quantity multiples on Shopify — enforced at checkout, no code required.
