A “buy 3 & save” offer works great for a serum. It falls flat for a t-shirt — nobody wants three of the same size. To make multi-buy work for apparel and footwear you need a per-unit variant selector: the shopper buys the pack, then picks a size or colour for each unit. This guide shows how to let customers mix variants in a bundle on Shopify and keep the discount checkout-safe.
Why the native quantity discount isn’t enough
Shopify’s automatic discounts and most quantity-break widgets add N of one variant to the cart. For a sized product that means the shopper has to add each size manually and hope the discount still triggers — friction that kills the offer. What you actually want is one offer that:
- Advertises the tier (“Buy 3, save 15%”) on the product page.
- Renders one variant dropdown per unit when a multi-unit tier is selected.
- Adds each chosen variant as its own line, yet still unlocks the tier discount.
How to set it up
- Install a product-page offer app that supports per-unit variants — our free Profit Flow AOV Bundle does this at no cost.
- Create a quantity (volume) offer on the product and set your tiers, e.g. Buy 2 save 10%, Buy 3 save 15%.
- Turn on per-unit variant selection. Now, when a shopper picks the “Buy 3” tier, the widget shows three dropdowns — one for each unit — listing the product’s sizes or colours.
- Publish and add three different sizes to the cart, then go all the way to checkout and confirm the discounted price holds.
That last step matters more than it looks.
Keep it checkout-safe
The risk with any variant bundle is that the discount is faked in storefront JavaScript — it looks right in the cart, then quietly disappears at checkout (or worse, a shopper games it). The fix is to enforce the offer with a Shopify Function: it re-reads the cart server-side, sums the product’s quantity across every variant line, and applies the tier discount only when the cart still qualifies.
Because the Function counts total quantity — not “3 of the same variant” — buying a Small, a Medium and a Large still counts as three units and unlocks the “Buy 3” price. And because it runs at checkout, the price the shopper saw is exactly what they pay.
When to use per-unit variants
- Apparel — buy 3 tees, pick a size each.
- Footwear / socks — multi-pair packs with a size per pair.
- Cosmetics with shades — buy 2 lipsticks, choose a shade each.
- Anything sold in a size or colour where variety, not repetition, drives the multi-buy.
Pair it with a free gift with purchase or a mix & match build-a-box for a complete product-page offer — all enforced at checkout.
Profit Flow AOV Bundle runs per-unit variant offers (and quantity breaks, BOGO, bundles and gifts) on any Online Store 2.0 theme, free. See it on your store →