Assigning One Size Chart to Hundreds of Products With Rules

Building a size chart is the easy part. The real work — the part that eats afternoons and breeds mistakes — is getting the right chart onto every product that needs it. Do it manually and a 500-product catalog becomes 500 edits, plus a fresh round every time you add stock. There's a smarter model: rule-based assignment, where you describe which products should get a chart and let the rules do the placing. This post shows how to think about assignment at scale so you can, as the saying goes, deploy once and forget.

The Problem With Manual Assignment

Attaching a chart product-by-product breaks down fast:

• It doesn't scale. Time grows linearly with catalog size. New arrivals mean new manual work forever.
• It drifts. Someone adds ten shirts on a busy day and forgets the chart. Now some products have guides and some don't, with no easy way to tell which.
• Updates multiply. Change your denim measurements and you're hunting down every affected product to confirm it points at the right chart.

Manual assignment treats each product as a special case when, in reality, products fall into a handful of natural groups.

Think in Groups, Not Products

Your catalog already has structure Shopify knows about — collections, product types, vendors, and tags. Rule-based assignment uses that structure so you assign a chart to a group definition instead of to individual items. Add a new product that matches the group, and it inherits the chart automatically. Supra Size Chart builds assignment around exactly these five rule types:

Each maps to a different way your catalog is naturally organized, and you can combine them to cover the whole store with just a few rules.

Matching Rules to Real Catalogs

Product Type for Broad Coverage

Product type is often the strongest starting point because it's stable and catalog-wide. One rule — type "Footwear" gets the shoe chart — covers every shoe you sell now and every shoe you'll add later. A handful of type rules can blanket an entire store:

• Type "Footwear" → footwear chart
• Type "T-Shirts" → slim tops chart
• Type "Outerwear" → outerwear chart

Vendor for Brand-Specific Sizing

Multi-brand stores live with the reality that brands size differently. A vendor rule pins each brand's own chart to its products — vendor "NorthPeak" gets NorthPeak's chart — so a shopper always sees measurements that match the actual garment, not a store-wide average.

Tags for Cross-Cutting Fit

Tags shine when the attribute cuts across categories. "Slim-fit" might apply to shirts, jackets, and trousers alike. A single tag rule — tag "slim-fit" gets the slim chart — reaches all of them at once, regardless of type or collection.

Collections for Merchandised Groups

If you already curate collections for how you sell, reuse them. A "Swimwear" collection rule attaches your swim chart to exactly the products you've merchandised together.

Specific Products for the Exceptions

Every catalog has oddballs — the one item that doesn't fit any group. A product-level rule handles it directly without disturbing your broader rules.

Handling Overlap: Precedence

The natural question: what happens when a product matches two rules? A jacket could be in the "Outerwear" type and carry a "slim-fit" tag. A sensible system resolves this with precedence — more specific rules win over broader ones. A typical order, from highest priority to lowest:

1. Specific product (most specific)
2. Tag
3. Collection
4. Vendor
5. Product type (broadest)

So your "slim-fit" jacket gets the slim chart even though a broader outerwear rule also matches. Understanding precedence lets you layer a broad safety-net rule underneath and narrow overrides on top.

A Practical Rollout Strategy

Here's a sequence that covers a large catalog quickly without gaps:

1. Blanket with type rules. Assign a chart to each major product type first. This alone catches the majority of products in a few rules.
2. Override by vendor where specific brands need their own measurements.
3. Layer tag rules for cross-cutting fits like slim or relaxed.
4. Handle exceptions with a few product-level rules for the true one-offs.
5. Verify coverage. Spot-check a product from each group and confirm the right chart renders.

Done in that order, a store of any size gets full coverage from a short, readable list of rules — not hundreds of edits.

Why This Saves You Time Later

The lasting payoff is what happens after setup:

• New products self-assign. Add a shoe, and if it's typed "Footwear," it inherits the chart with zero extra steps.
• Updates are central. Change one chart and every product its rule touches updates at once — no hunting.
• Coverage is auditable. A list of rules is far easier to reason about than an implied mapping scattered across products.

Combined with charts stored as your own Shopify metaobjects, the whole system stays fast — Supra Size Chart resolves rules and renders server-side with Liquid, so shoppers get the right chart instantly on every matching page.

The Takeaway

Assigning size charts one product at a time is a tax that compounds with every new arrival. Rule-based assignment flips it: describe your product groups once with collection, type, vendor, and tag rules, let precedence sort out overlaps, and let new products inherit the right chart on their own. Set it up thoughtfully and you really can deploy once and forget.