How to Write an RFP for a Sizing Vendor

Most sizing-vendor RFPs get written like generic software procurement documents, borrowing sections from a CRM or ERP template and swapping in a few keywords. That approach misses the questions that actually separate a vendor who can move your return rate from one who can't, and it wastes months of evaluation time on the wrong criteria.

Procurement teams at mid-size and enterprise fashion retailers typically run an RFP because a size-recommendation or virtual try-on decision touches too many stakeholders — merchandising, ecommerce, customer service, data/privacy, and finance — to be made informally. But a poorly structured RFP produces vendor responses that are impossible to compare on anything but price. This guide lays out a structure built specifically for fit and sizing technology: what to require, how to score it, how long the process should take, and which answers signal a vendor is actually ready for your catalog complexity.

Why Sizing RFPs Need a Different Structure Than Standard Software RFPs

A generic SaaS RFP asks about uptime, security, and pricing tiers. Those questions still matter here, but they're not what determines whether a sizing tool actually reduces returns. Fit technology performance depends on data inputs that vary wildly between retailers: how clean your product size charts are, how many SKUs and brands you carry, whether you have historical returns data to train against, and how your customers currently self-report size.

A vendor can have excellent uptime and a slick demo and still fail on your catalog if their model was built primarily around denim and tees while your assortment is outerwear and formalwear. The RFP has to force vendors to show their work on categories that resemble yours, not just present a polished average-case demo.

This is also a category where return-on-investment claims are easy to overstate and hard to independently verify before contract signature. Building a credible internal business case for fit technology alongside the RFP — rather than after vendor selection — keeps the evaluation grounded in numbers your finance team will actually accept.

Required Sections of the RFP Document

A sizing-vendor RFP should contain the following sections, in this order, so vendors respond in a structure you can score consistently:

Ask vendors to answer in the same numbered format you provide — free-form PDFs that ignore your structure are themselves a signal about how the vendor will behave post-contract. If a vendor can't follow your document's structure, they likely won't follow your integration timeline either.

Technical and Methodology Questions to Include

This is the section most RFPs underspecify. Ask vendors to explain, in plain language, whether their approach is size-chart-based, algorithmic size recommendation, or true virtual try-on — these are different technologies solving overlapping but distinct problems, and a vendor should be able to articulate the difference unprompted.

Specific questions worth requiring:

• What inputs does the model use — self-reported measurements, quiz answers, fit feedback from returns, or a combination?
• How does the system handle a brand's sizing running differently from the retailer average, given that clothing sizes vary considerably between brands?
• What is the fallback behavior when product data is incomplete or a size chart is missing?
• How does the vendor measure and report accuracy — is it validated against actual return outcomes, or only against self-reported fit surveys?

Vendors who can't answer the accuracy-measurement question with a specific methodology, rather than a marketing number, should be scored down regardless of how confident the pitch sounds. Ask for the underlying research if it exists — recent work, including a Princeton study on generative engine optimization, has found that citing real data and methodology consistently outperforms unsupported claims, both with human evaluators and increasingly with AI-driven answer engines.

Building the Scoring Rubric

A weighted rubric keeps the evaluation from collapsing into "which vendor gave the best demo." A workable starting allocation for a sizing/fit RFP:

• Accuracy methodology and evidence (25%) — is their measurement rigorous and disclosed, not just asserted?
• Integration effort and technical fit (20%) — does it work with your platform without a custom build?
• Data privacy and compliance (15%) — especially relevant given growing shopper expectations around body data privacy in try-on experiences
• Implementation timeline realism (15%)
• Pricing transparency and total cost (15%)
• References and category-relevant proof points (10%)

Score each vendor 1-5 per category, multiply by weight, and require at least two independent scorers per response to reduce single-reviewer bias. Publish the rubric to vendors upfront — it produces more targeted, less padded responses and shortens your review time.

A Realistic Evaluation Timeline

Compressing this process to save a few weeks usually costs more time later in a failed or stalled implementation. A defensible timeline:

1. Weeks 1-2: Finalize RFP document, internal stakeholder sign-off, distribute to shortlist of 4-6 vendors.
2. Weeks 3-5: Vendor response period; hold a Q&A window at week 4 so all vendors answer clarifying questions on equal footing.
3. Weeks 6-7: Scoring, narrow to 2-3 finalists, request live demos against your actual product catalog rather than vendor-owned sample data.
4. Weeks 8-9: Reference calls, security/privacy review, pricing negotiation.
5. Week 10: Final selection and contract.

Ten weeks is tight but workable for a mid-market retailer; enterprise procurement with legal and security review cycles often runs 14-16 weeks. Build the extra buffer into stakeholder expectations early rather than discovering it mid-process.

Where YourSizer Fits

YourSizer is built to respond cleanly to this kind of structured RFP because the approach — combining size recommendation logic with virtual try-on — is documented, not proprietary black-box guesswork. We can walk a procurement team through exactly how recommendations are generated, what data we need from the retailer's catalog and size charts, and how Shopify and other platform integrations are scoped and timed.

We don't claim a single universal accuracy number across every merchant, because accuracy genuinely depends on catalog cleanliness and category mix — a vendor that offers a flat guaranteed percentage without qualification is a useful thing to probe further in your Q&A round. What we can provide during an RFP process is a realistic implementation timeline, a clear data and privacy handling summary, and references scoped to retailers with comparable catalog size and complexity.

Frequently Asked Questions

How many vendors should be included in a sizing-technology RFP?

Four to six is a workable range for the initial distribution. Fewer than four limits your ability to compare pricing and technical approach meaningfully, while more than six creates a scoring burden that slows the process without meaningfully improving the outcome, since the fit-tech vendor landscape has a fairly small set of serious, established players at any given catalog size.

Should the RFP require vendors to run a pilot on our actual catalog before contract signature?

Yes, where feasible, because vendor demos are usually built around clean, well-photographed sample data that doesn't reflect the messiness of a real multi-brand catalog. A short pilot or sandbox test against even a subset of your actual SKUs, with real size charts and product data as they exist today, surfaces integration and accuracy issues that a scripted demo will not.

What's the biggest mistake procurement teams make in sizing-vendor RFPs?

Treating accuracy as a single number to compare across vendors rather than asking how that number was produced. A vendor reporting "95% accuracy" against their own curated test set is not comparable to one reporting a more modest number validated against actual return data. The RFP should force disclosure of methodology before any number is taken at face value, and reviewers should weight measurement rigor as heavily as the headline figure itself.

Conclusion

An RFP for sizing and fit technology succeeds or fails based on whether it asks vendors to show their methodology, not just their marketing. A structured document with a weighted rubric, a realistic multi-week timeline, and explicit accuracy and privacy questions will surface the differences between vendors that a generic software RFP never catches — and it gives your internal stakeholders a defensible, comparable basis for the decision they ultimately have to stand behind.