Disclosure: this article is published by Fitle, which makes one of the apps compared here. The facts quoted (prices, reviews, languages, features) come from public Shopify App Store listings and vendor websites, checked on 3 November 2026. Where we share our own reading of the market, we say so.
For fashion stores, size is the number one reason for returns. A Coresight Research study published in May 2026 (sponsored by sizing specialist Alvanon) estimates the online apparel return rate in the US at around 23% in 2025, with nearly 70% of shoppers who returned clothing citing size or fit. Every return you prevent before checkout is a sale kept, one less parcel, and a happier customer.
That is what a size recommendation app is for: helping shoppers pick the right size before they order. But they don’t all work the same way, and they don’t suit the same kind of store.
Two recommendation methods, and what they mean for you
- Recommendations based on your size charts. Shoppers enter a few details (height, weight, age, fit preference) and the app matches them to your measurement charts. Upside: it follows your exact patterns. Downside: you need to build and maintain a reliable chart for each product or collection, and map it to your products.
- Recommendations based on a fit questionnaire. Shoppers answer a few questions about their body shape and habits, without measuring themselves, and the app relies on fit data or on what similar shoppers bought. Upside: little setup on your side. Downside: accuracy depends on the quality and volume of the data behind it.
No size chart yet? It is no longer a prerequisite: with a fit questionnaire, you can now offer accurate size recommendations without building or maintaining a chart.
Our comparison criteria
- Method: size charts, fit questionnaire, or both?
- Setup and support: what you have to configure yourself, and what help you get.
- Languages: is the widget available in your shoppers’ language, and from which plan?
- Pricing model: flat subscription, per order, per visitor or per add-to-cart.
- Reviews: Shopify App Store rating and number of reviews. Below 10 reviews, a rating tells you little.
Comparison table
| App | Method | Widget in French | Support in French | Shopify reviews | Price (USD, per listing) |
|---|---|---|---|---|---|
| Kiwi Size Chart & Recommender | Recommendations based on size charts (height, weight, age, fit preference), on higher plans | Via auto-translation, on higher plans | Not stated | 4.7 / 1,242 reviews | Free; $7.99 to $26.99/mo |
| Fit Quiz (Easysize) | Fit questionnaire, no size chart or measurements | “20 languages” per description | Not stated | 4.1 / 38 reviews | $35 to $250/mo + $0.15 per add-to-cart of the recommended size |
| Sizebay | Recommendation based on your size charts | Yes | No | No reviews yet | Not listed (quote-based) |
| AI Fit Finder (CartCoders) | Recommendations based on size charts (height, weight, age) | Yes, on L and XL plans | Not stated | 5.0 / 21 reviews | $9.99 to $99.99/mo |
| Smart Size AI Fit Recommender | Hybrid: size charts and fit questionnaire | Yes | Not stated | 5.0 / 6 reviews | Free (50 users/mo); $29 to $89/mo |
| Fitle Size Recommender | Fit questionnaire + recommendations based on your size charts (Gold plan) | Yes, FR + EN on the free plan | Yes, team based in France | No reviews yet (launched May 2026) | $0/mo + $0.20/order; $55 or $223/mo + lower per-order fees |
Prices and reviews checked on 3 November 2026 on the Shopify App Store; they change often.
Which app for which store size?
According to an analysis by Fitle based on Wappalyzer data (2026), more than half of the roughly 6,900 stores using Kiwi have no traffic measurable by the tool: most of them are small stores. Sites using Easysize (about 150) or Sizebay (about 530) have higher estimated traffic. The 123 sites using Fitle have a median estimated traffic more than twenty times higher than Easysize or Sizebay sites: Fitle’s engine was first built for major brands, and its Shopify app makes it available to smaller stores.
The apps in detail
Kiwi Size Chart & Recommender: the go-to size chart app on Shopify
Around since 2018 and built only for Shopify, Kiwi is the most installed and most reviewed app on this list. Its strength is size charts: ready-made templates, import from a CSV or an image, automatic unit conversion, and rules to apply a chart to a whole collection. Higher plans add recommendations based on size charts: the shopper’s height, weight, age and fit preference are matched to your charts.
Setup is self-service: you build your charts and map them to your products. Help comes from the support team (chat, email), with no dedicated expert to review the tool’s performance with you. In our experience of the market, Kiwi is mostly chosen to display clear size charts, by new or low-volume stores. As traffic grows, many brands we meet keep Kiwi for the chart and add a more advanced recommendation tool. Best for: stores starting out that want a clean size chart, fast and cheap.
Fit Quiz (Easysize): recommendations without a size chart
Built by Copenhagen-based Easysize, Fit Quiz asks shoppers a few questions, with no measurements, and doesn’t rely on your size charts, so setup takes less preparation. Recommendations are based on custom fit rules; Easysize doesn’t highlight machine learning on its pricing page. Support is by email and chat (plus phone from the Pro plan), with no dedicated expert to follow the tool’s performance. Watch the pricing model: on top of the subscription, $0.15 is charged every time the recommended size is added to cart, whether or not the order goes through. Best for: mid-sized stores that want to start without a size chart.
Sizebay: recommendations based on your size charts, strong in South America
Founded in Brazil, Sizebay offers size recommendations based on your size charts, with a widget available in French. It isn’t Shopify-centric and also runs on other platforms. According to an analysis by Fitle based on Wappalyzer data (2026), a large share of the sites using Sizebay run neither on Shopify nor on a major commerce platform, but on e-commerce platforms built for small and mid-sized stores and widely used in Brazil (Nuvemshop, Tray, Magazord and others), with low estimated traffic. Its Shopify app arrived in June 2026: no reviews yet, and the listing shows no pricing grid (quote-based subscription). Best for: small and mid-sized multi-platform stores, mostly in South America.
AI Fit Finder (CartCoders): the same approach as Kiwi
AI Fit Finder follows the same positioning as Kiwi: recommendations based on size charts. Shoppers enter their height, weight and age, which are matched to your charts, which you need to build and map to your products. Pricing depends on the number of active products, and multi-language support only comes with the L plan. Best for: small and new stores that want a simple recommendation at a predictable price.
Smart Size AI: a hybrid between Kiwi and Easysize
Smart Size AI combines both approaches: size charts, like Kiwi, and a fit questionnaire, like Easysize. It is well rated, but on few reviews. Its free plan covers 50 users per month. Best for: small stores that want to try both methods on a controlled budget.
Fitle Size Recommender: big-brand accuracy for Shopify stores
Fitle is a French company specialised in sizing for fashion. Since 2013, Fitle has worked with more than 300 fashion brands, including major retailers and marketplaces, to reduce size-related returns and improve conversion. Fitle was also named “Best Size Recommendation SaaS” in 2025 and 2026 by Acquisition International. In 2026, it also won “Best Apparel Size Recommendation SaaS” at The SaaS-ies. Beyond this recognition, Fitle asks its users whether it makes their shopping journey easier. Over the past two years, 216,791 unique users have given it an average rating of 4.8/5 (November 2026). The Shopify app, launched in May 2026, brings that same level of accuracy and support to stores with more modest traffic. It integrates as a native Shopify app block: you add it to your product page from the theme editor, like any other block, with no code or extra script added to your site.
Fitle combines both methods: a fit questionnaire and a recommendation engine based on size charts (from the Gold plan). Fitle even offers a third model, based on the non-returned purchase history of a store’s customers (social proof); this engine isn’t available through the Shopify plans, though. Another difference from other solutions: on the Gold plan, a sizing expert from the Fitle team reviews the tool’s performance with you, in French or English, whereas most apps stop at chat or email support. The widget works in French and English on the free plan, and pricing scales with your volume: you pay per order, with a unit cost that drops as you grow. A 14-day trial is available on paid plans. Best for: fashion brands that want accurate recommendations now, without waiting to reach enterprise-level volume. Discover Fitle AI Reco.
What about large brands?
The biggest fashion sites often use custom-integrated solutions outside the Shopify App Store. That is Fitle’s original segment: it has served major brands for years. Virtusize, a Japanese vendor available on Shopify, is geared towards Asian markets: its listing only shows English and Japanese.
Summary: methods, size charts and store size
| Solution | Recommendation method | Size chart required? | Typical store size* | Support |
|---|---|---|---|---|
| Kiwi | Recommendations based on size charts (higher plans) | Yes | Small and new stores | Chat / email support |
| Fit Quiz (Easysize) | Fit questionnaire | No | Mid-sized stores | Email / chat support (phone from Pro) |
| Sizebay | Recommendation based on size charts | Yes | Small and mid-sized stores, mainly in South America | Chat and email support, no dedicated support |
| AI Fit Finder (CartCoders) | Recommendations based on size charts | Yes | Not measured | Chat / email support |
| Smart Size AI | Hybrid: size charts and fit questionnaire | Depends on the mode used | Not measured | Not stated on the listing |
| Fitle | Fit questionnaire + size charts (Gold plan); social proof (outside Shopify plans) | No (optional) | From major brands to smaller stores (via the Shopify app) | French-language support + sizing expert who follows the tool’s performance (Gold plan) |
* Based on Fitle’s Wappalyzer analysis (2026); “not measured” when the app isn’t covered. Smart Size AI and AI Fit Finder are not yet among the technologies detected by Wappalyzer, a sign of a still limited installed base.
How to choose for your store
- You don’t have a size chart: either build one (Kiwi is a good option to display it), or go straight to a questionnaire-based recommendation, which works without a chart.
- Size-related returns are eating into your margins: move to a real recommendation, and pick the method based on how much time you can spend on your size charts.
- You sell in several languages: check from which plan your language is included and test the widget on your theme.
- Your volume swings a lot (sales, Black Friday): compare the real yearly cost of a flat subscription, per-order pricing and per-add-to-cart pricing.
- You want hands-on support: most apps offer chat or email support. Few give you access to an expert who reviews the tool’s performance with you (Fitle’s Gold plan does). Also check who configures the solution, you or the vendor.
Whatever you choose, test it on a few best-sellers and track two metrics over at least one return cycle (30 to 60 days): conversion rate on equipped product pages, and return rate for the “size” reason.
Size isn’t everything: the role of product visuals
Shoppers also return clothes because they don’t look like what they imagined. Photos showing the product worn, from several angles and on different body types, help them picture it: they buy something they are more likely to love when it arrives. Combining the right size with the right visuals improves conversion and reduces returns at the same time. That is the idea behind our AI photo studio.
FAQ
Do you need a size chart to use a recommendation app?
Not always. Questionnaire-based tools (such as Easysize) work without one; chart-based tools (Kiwi, Sizebay, AI Fit Finder) need it; Smart Size combines both approaches. Fitle does both: its questionnaire-based recommendation works without a chart, and it can also use your size charts if you have them (Gold plan of the Shopify app). Either way, up-to-date measurements improve accuracy.
Can I keep Kiwi and add a recommendation tool?
Yes. Many stores keep their size chart for shoppers who like to measure themselves, and add a recommendation widget for everyone else.
Do these apps slow down product pages?
Shopify apps that integrate through theme app extensions load without editing your theme code and are removed cleanly if you uninstall them, so their impact on speed is usually limited. For solutions integrated through a script added to your theme, and to be safe for all of them, test your product page speed before and after installing, for example with PageSpeed Insights.
Sources: Shopify App Store listings checked on 3 November 2026 (Kiwi, Fit Quiz, Sizebay, AI Fit Finder, Smart Size, Fitle); Kiwi Sizing, AI Size Recommender; Easysize pricing; FashionUnited, Coresight Research study (June 2026).
