A size chart is one of the most effective tools a fashion e-commerce store has. It solves a single, recurring problem: shoppers don’t know what size to order. Sizing is inconsistent across brands, so the size a customer wears elsewhere tells them very little about what to order from a new store.
A size chart closes that gap by listing the body measurements that correspond to each size. Done well, it increases conversions, lowers return rates, and teaches shoppers how a brand’s garments actually fit. Done poorly, it creates the same confusion it was meant to prevent.
That happens with garment measurements instead of body measurements, or with one sitewide chart covering products that don’t share the same fit.
This guide was built with input from Sizebay’s in-house patternmaking team. It covers what size charts are and why accuracy matters more than most stores assume. You’ll also learn how to build one from scratch and where a size chart alone stops being enough.
What Is a Size Chart?
A size chart is also called a sizing guide or measurement table. It lists a garment’s available sizes next to the body measurements each one is built to fit. The goal is to replace guesswork with a direct comparison.
So, in order to find out what size fits better, the shopper takes their own measurements, or uses a simpler proxy like height and weight. They then match that to a size, instead of assuming their size in one brand carries over to another.
That said, a size chart is not a complete solution on its own. It’s cheap to implement and easy to scan, which is why nearly every fashion retailer uses one. But it can’t account for two things that matter just as much as the numbers themselves. Those are how loose or tight a shopper likes to wear a piece, and how a given fabric behaves.
For example, a stretch legging and a stiff denim jean call for very different reading of the same measurement. A chart gets a shopper close to the right size; it doesn’t guarantee a perfect one.
Internal vs. External Size Charts
It’s also worth separating what this guide covers from what it doesn’t. Internal size charts are confidential documents used during manufacturing. They hold exact garment measurements tied to pattern grading, closely guarded as part of a brand’s fit and shape.
External size charts, the subject of this guide, are the public-facing tables customers see on product pages. They translate those internal specs into something a shopper can act on.
Should a Size Chart Use Body or Garment Measurements?
The most consequential decision in building a chart is whether to list body measurements or garment measurements. It’s exactly where many stores get it wrong.
Garment measurements describe the piece as it was cut and sewn, but the body measurements describe the person wearing it. The two diverge wherever stretch, ease, or an oversized silhouette is part of the design.
That means a shopper comparing garment measurements directly against their own body is often working from the wrong reference point entirely.
The failure mode is predictable. A shopper with a 28-inch waist sees a stretch legging listed at 24 inches and sizes up. The legging was designed to sit tighter than the body it fits. Another sees an oversized jacket’s chest measurement well above their own and sizes down, missing the loose fit the design intended.
Both shoppers followed the chart correctly and still ended up with the wrong size. The problem wasn’t an error on their part, but a number that was never meant to be compared that way.
Body measurements avoid this failure because they describe something fixed: the shopper’s own body, independent of fabric, cut, or design intent. That’s why every recommendation in this guide, and every well-built chart, starts from the body, not the garment.
Why Does an Accurate Size Chart Matter for E-commerce?
The business case for getting this right is direct. Sizing uncertainty is one of the clearest, most fixable reasons shoppers abandon purchases or send them back.
Roughly one in three shoppers abandon their cart specifically because they’re unsure which size to order. That hesitation is exactly the point a clear, accurate chart removes. The returns data makes the same point from the other direction.
In a Coresight Research study, 53% of respondents cited size or fit as their top reason for returning an item. A McKinsey & Company report conducted with online retailers found that figure climbing as high as 70%. In other words, most returns aren’t really about the product. They’re about a shopper guessing wrong on size, exactly what a size chart is built to prevent.
There’s a third, less obvious benefit: a size chart teaches shoppers how a brand fits, and that benefit compounds over time. A first-time customer has no reference for how your garments run relative to the number on the label. That’s because sizing is notoriously inconsistent across the industry. A clear chart gives them that reference immediately. That matters more for cart conversion on a first purchase than almost any other piece of product-page content.
| Size | Bust (in) | Waist (in) | Hip (in) |
| S | 34 | 26 | 37 |
| M | 36 | 28 | 39 |
| L | 38 | 30 | 41 |
| XL | 40 | 32 | 43 |
How to Create Size Charts
Creating size charts can take a little time, but the process is very straightforward. Here’s how you can create size charts for your fashion e-commerce store:
Common Mistakes When Building a Size Chart
Using only S, M, and L, with no numbers. Generic sizing varies from brand to brand and doesn’t help a shopper decide anything. Every size chart needs measurements in inches or centimeters next to the letter, not just the letter alone.
Measuring only one sample per size. Relying on a single reference garment hides normal variation in cut. Whenever possible, measure more than one unit of the same size before finalizing the chart.
Forgetting to update the chart after switching suppliers. A change in factory or pattern alters grading, even when the size name stays the same. When that happens, the old chart becomes a source of error instead of help.
Mixing body measurements and garment measurements in the same column. This confuses shoppers and distorts their size choice. Pick one standard, body or garment, and keep it consistent across the whole chart.
What Are the Best Practices for a Size Chart People Actually Use?
A few practical principles turn a correct chart into one that shoppers actually use well.
Match the Chart to the Product, Precisely
Two separate issues come up here, and both cause the same kind of frustration. First, don’t publish one master document covering every product category and link to it from every page. A shopper on a sweater’s product page should only see sweater sizing, not your entire catalog’s charts mixed together. Second, within that product-specific chart, show only the measurements relevant to that garment. Use upper-body numbers for tops, lower-body for bottoms, and both for a dress or jumpsuit. A shopper buying pants has no use for a sleeve-length column. Digging through irrelevant numbers to find the one that matters, on top of that, undermines the quick, effortless experience a chart should deliver.
Design for People Who Don’t Own a Measuring Tape
Most shoppers can’t tell you their waist or hip measurement off the top of their head. Fewer still have a tape measure within reach while browsing. Including height and weight alongside the standard measurements gives those shoppers a way in without requiring them to measure anything. Where you do ask for a measurement, pair it with a short instruction, ideally an image, on exactly where it’s taken. “Waist” means different things to different people. A shopper measuring in the wrong spot will land on a confident, wrong answer. All of this needs to hold up on a phone screen, since that’s where most shoppers are reading it.
Keep an Internal Record of Which Chart Applies Where
This one is for your team, not your shoppers, but it prevents a specific, recurring problem. A spreadsheet mapping every chart to the products that use it means whoever loads a new product knows which chart to assign. That knowledge, as a result, doesn’t disappear when someone leaves the team.
Treat the Chart as a Floor, Not a Ceiling
Even an accurate, well-designed chart leaves some shoppers unsure, that’s a structural limit of static tables, not a sign the chart failed. What to do about that gap is covered next.
Let Sizebay Build (and Maintain) This For You
Everything above works, but it’s also a real operational lift. There’s fit models to source and measurements to re-check whenever grading isn’t linear. On top of that, there’s a chart to redesign per category and an internal record to keep current as your catalog grows. For a lean team, that’s a lot of recurring work sitting on top of the actual job of running a store.
Sizebay has handled exactly this for over 15 years, and more than 1,200 fashion retailers currently rely on us to do it. Instead of building fit models, grading ranges, and charts internally, our in-house team of patternmakers manages that entire process for your catalog. That work runs from the initial measurements through the finished chart published on your site. It also pairs with Sizebay’s virtual fitting room, so shoppers get a size recommendation instead of a table to interpret. The chart still does the underlying work; your team and your shoppers just don’t have to do it manually.
Converting Sizes Across Regions
If your store sells internationally, or draws shoppers from more than one country, it helps to include a conversion reference alongside your size chart. The figures below are approximate and vary by brand grading, but they’re a reliable starting point.
| US | UK | EU | Brazil |
| 4 | 8 | 36 | 36 (P) |
| 6 | 10 | 38 | 38 (M) |
| 8 | 12 | 40 | 40 (G) |
| 10 | 14 | 42 | 42 (GG) |
This kind of conversion works best when the source chart is built on body measurements rather than garment measurements. A reference tied to one region’s cut loses accuracy once it’s adapted to another standard.
Ready to Build Yours?
You now have everything needed to build an accurate, body-measurement-based size chart for your store. Or you can use it to confirm the one you already have is pulling its weight. If you’d rather have Sizebay’s patternmaking team build and maintain it for you, get in touch.
We’ll pair it with a virtual fitting room that puts shoppers into the right size automatically. And we’ll walk you through how it works for your catalog.
