How Stores Map Body Measurements to Their Own Size Chart

Stores map body measurements to their own size chart by comparing each key measurement, such as chest, waist and hips, against the range for every size, then picking the size where all of them fit. When measurements point to different sizes, the store's rule decides, and the safest rule is to size up to the largest one.

That simple idea sits behind every size recommendation tool. This guide shows the logic step by step, with a worked example you can test on your own chart. For the bigger picture of how photo-based sizing works, start with the guide to AI size recommendation for fashion stores.

What does "mapping" a measurement to a size mean?

Mapping means turning a number, like a 92 cm chest, into a label, like "M" or "UK 12". The number describes the shopper's body. The label is your brand's promise about the garment.

A size chart is the bridge between the two. Each row is a size, and each column is a body measurement with a minimum and a maximum. Mapping is just finding the row whose ranges contain the shopper's numbers.

This is why brand charts matter. Two stores can both sell a "medium" that fits very different bodies. The comparison of generic and brand-specific charts explains why your own chart gives a better answer than a standard one.

Which measurements decide the size for each garment type?

Not every measurement matters for every garment. Good mapping only looks at the ones that control fit.

Garment type	Measurements that usually decide fit
Tops	Chest
Outerwear	Chest, sometimes with room for layers
Dresses	Chest, waist and hips
Bottoms	Waist and hips

This is why ZeDaq.ai uses one chart per garment type: tops, outerwear, dresses and bottoms. A coat and a T-shirt from the same brand often fit differently, so each gets its own ranges.

How does the matching logic work step by step?

Here is the logic most sizing tools follow, written so you can check it by hand.

1. Collect the measurements. The shopper enters them, or a scan estimates them. With ZeDaq.ai, the shopper uploads one photo and types their height, and the measuring runs on their own device.
2. Pick the chart. Use the chart for the product's garment type.
3. Check each measurement on its own. For every relevant column, find the size whose range contains the number.
4. Compare the results. If every measurement lands in the same size, that is the answer.
5. Apply the tie rule. If they land in different sizes, choose the largest. A garment that is slightly loose can be worn or altered. One that is too tight usually comes back.
6. Handle the edges. If a number falls in a gap between two sizes, choose the larger one.
7. Show one label. Display the size exactly as your chart names it.

A worked example

Below is an example dress chart. It is an example chart only, so check your brand's own chart.

Size	Chest (cm)	Waist (cm)	Hips (cm)
S	84–88	66–70	90–94
M	88–93	70–75	94–99
L	93–98	75–80	99–104
XL	98–103	80–85	104–109

A shopper measures 90 cm at the chest, 74 cm at the waist and 101 cm at the hips.

• Chest 90 falls in M.
• Waist 74 falls in M.
• Hips 101 fall in L.

The measurements disagree, so the tie rule applies. The largest result is L, so the recommendation is L. If the shopper chose M, the dress would likely feel tight across the hips.

What goes wrong when mapping is set up badly?

Most bad recommendations come from the chart, not the math. Watch for these problems:

• Gaps between sizes. If M ends at 93 and L starts at 95, a 94 cm shopper has no size. Make the ranges meet.
• Garment measurements in a body chart. A flat width of 50 cm across the garment is not a 50 cm chest. Enter the body that fits the garment.
• One chart for everything. A fitted shirt and an oversized hoodie need different ranges.
• Mixed units. Pick centimeters or inches per chart and stick to it.

If you sell items with no chart at all, read what happens when a store has no size chart. With ZeDaq.ai, shoppers then get a size from a generic UK, US, EU or AU chart instead of your own.

How do you set up your own chart in ZeDaq.ai?

You enter your size guide once, and the scan uses it for every product of that type.

1. Open Dashboard → Size charts, or the size chart screen in the Shopify app.
2. Choose a garment type: tops, outerwear, dresses or bottoms.
3. Enter the minimum and maximum for each size and measurement.
4. Use your brand's own labels, such as "S, M, L" or "UK 8, UK 10".
5. Test with a few real body measurements from your team before you save.

The scan then recommends your labels and sizes up to the largest relevant measurement, the same way as the worked example above.

Does better mapping help with returns?

Wrong size is a common reason shoppers send clothes back, so a clear match between body and label helps shoppers order once. Mapping is only one part of the picture. Seeing the garment on their own body helps too, which the guide on how try-on can lower returns covers in more depth.

You can try both on the Free plan, which includes 3 try-ons and 3 measurements a month. Paid plans start with Micro at $14 a month, and see current plans and pricing for the rest.

FAQs

Why size up instead of down when measurements disagree?

A slightly loose garment is easier to wear, belt or alter. A tight one often can't be fixed, so sizing up is the safer default.

Do I need every measurement in my chart?

No. Include the measurements that decide fit for that garment type. A tops chart can work with chest alone.

Can I use my brand's own size names?

Yes. The recommendation shows the label exactly as you enter it, whether that is "M", "UK 12" or "Size 3".

What if my sizes run small?

Enter the body measurements that actually fit each size, not the ones printed on an old label. The mapping then reflects how your clothes really fit.