30 ml to 50 ml, One Tap: A Bigger-Size Upsell

Introduction

Some upgrades are not a different product. They are the same product, bigger.

The 50 ml instead of the 30 ml. The 1 kg instead of the 500 g. The customer has already chosen the formula, the scent and the brand. The only open question is how much of it they buy, and that question is usually answered by whichever size the variant selector shows first.

The instinct in most planning meetings is to fix it with design:

"Let's make the 50 ml the default selection."

A solutions architect asks a plainer question first:

"What would actually convince someone the bigger size is the better deal?"

A default is a nudge nobody notices. A sentence with the real price difference is an argument. This case study designs a size upgrade for a skincare brand whose customers kept buying the smallest bottle simply because it was selected by default.

Merchant Scenario

Consider Verdant Botanicals, a fictional Shopify brand selling plant-based serums and oils.

The hero serum came in 30 ml at $38, 50 ml at $54 and 100 ml at $92. Seventy percent of orders were the 30 ml. The 50 ml was the better deal per millilitre and the better margin. The variant selector did not say so.

The Variant Selector Problem

A size dropdown lists sizes. It does not say "the 50 ml is only $16 more." It does not say "and it costs less per millilitre."

Verdant wanted one line on the page that made the bigger bottle the obvious choice, without changing the product, the prices or the theme.

Business Objectives

Evaluating the Options

Option 1: Rely on the Variant Selector

Option 2: Upsell in Better Product Mode

Option 3: Upsell in Bigger Variant Mode

Comparison Matrix

The Discount Prime Configuration

One product. Bigger variant mode. The upgrade candidates were the product's own larger sizes, so there was no Upgrade To list to maintain.

Why Upsell Fits a Bigger-Size Upgrade

Bigger variant is the Upsell mode for upgrading within one product. The builder looked at the Hero Serum's options and found one whose prices increased along it: Size. 30 to 50 to 100 ml, $38 to $54 to $92. That is a price-ordered option, and it is exactly what the mode needs.

The customer keeps every other choice they made. Same scent, same formula. Only the size moves.

Had the product's only option been a scent with flat pricing, the builder would have said so: no option whose prices increase, nothing "bigger" to offer, switch to Better product mode.

The Ladder, Not Just the Next Step

The upgrade was always the next rung, with {diff} resolved to the real gap.

The Banner Under the Buy Button

On the serum page, below Add to cart:

Upgrade to Hero Serum 50 ml - only $16 more

One tap changed the selected variant and the price. No cart visit needed. In the cart, the same offer appeared as a swap card for anyone who had added the 30 ml from elsewhere, such as a quick-add button on a collection page.

Customer Journey

1. A shopper opens the Hero Serum page with 30 ml selected.
2. Below Add to cart, the banner offers the 50 ml for $16 more.
3. They tap it. The selected variant changes to 50 ml and the price updates to $54.
4. A second shopper quick-adds the 30 ml from a collection page and goes straight to the cart.
5. The cart swap card offers the same upgrade. They tap Switch and the 30 ml line becomes the 50 ml, with undo visible.

What Bigger Variant Cannot Do

It cannot offer a different product. A customer buying the Hero Serum could be moved to the bigger Hero Serum, never to the premium Night Serum. That is Better product mode, as in The Derby and the Loafer, and Verdant ran a second campaign for it.

The mode also depends on prices actually increasing along an option. When the 100 ml went on sale below the 50 ml, the ladder broke for that step. The builder warned, and the sale was adjusted.

Metrics That Measure Success

• Share of serum orders on the 30 ml, 50 ml and 100 ml, month over month
• Banner tap rate on the product page and swap rate in the cart, tracked separately
• Estimated Profit per serum order, from real Shopify cost prices
• Average order value against the $52 store baseline
• Reorder interval for 50 ml buyers compared with 30 ml buyers

Common Mistakes

• ❌ Using Better product mode for a size upgrade, and listing each size as a separate "product" to offer.
• ❌ Choosing Bigger variant for a product whose only option is color or scent, where no size is bigger.
• ❌ Running a sale on a large variant that drops it below a smaller one, and silently flattening the ladder.
• ❌ Writing a phrasing template without {diff} for an upgrade where the small price gap is the whole argument.
• ❌ Forgetting the cart swap card, and missing the customer who added the small size from a quick-add button.

Key Lessons

The size dropdown was the problem. It listed options. It did not recommend one.

A single line with the real price difference did what the dropdown never could, and Bigger variant mode kept that line correct for every size the customer started from.

Conclusion

The bigger bottle was always the better deal. Nobody said so.

Upsell with Bigger variant mode finds the price-ordered option, offers the next size up, and puts the difference in front of the customer. In this scenario, Verdant's 30 ml share of serum orders dropped from 70% to 44%. The 50 ml became the default by persuasion, not by selector.