Why the same body gets a different size
Take one shopper. Chest 96 cm, waist 78 cm, hip 102 cm. Put them in three of your products that share a size run:
- a rigid shirt cut to sit close
- a jersey with real stretch
- an oversized hoodie meant to hang off the shoulder
The body did not change. The correct size did. A Size Chart that maps 96 cm to M on all three will be right once and wrong twice, and the shopper will blame “your sizing.”
Fit is garment minus body. A chart that ignores the difference will recommend a size the design never intended.
That difference is ease: the centimetres of room between the person and the cloth. Stretch changes how much of that room the fabric can give. The cut changes how much room you meant to leave. Both belong on the chart, next to the numbers, or the recommendation is just the numbers read literally.
Two kinds of chart, then two fields
If the chart says “if your body measures this, buy this size,” you are on a body Size Chart. The shopper’s chest, waist, and hip compare straight to the row. Ease is already baked into how you built the row. You do not add a second interpretation on top.
If the chart says “this is how big the garment is,” you are on a garment Size Chart. Now the app has to translate cloth into a body. A flat chest width is doubled to a circumference when it really is a half-measure. Then two fields, per chart, finish the translation:
Fit intent. How the piece is designed to sit: tight, regular, relaxed, or oversized. Tight aims snugger. Oversized aims roomier, so the same body is pointed at a larger size than the raw centimetres suggest. This is the garment’s intent. The shopper can still say they prefer a slimmer or looser fit on top of it.
Stretch. How much the fabric gives, from 0% to 20%. Zero is rigid. Around 10% is slight give. Around 20% is very stretchy. Stretch widens the garment before it is compared to the body, so a stretch piece can fit a larger body than its flat measurement implies, and the recommended size can come down.
Both fields live on garment charts only. A body chart leaves them empty, because the row is already the answer.
We kept it to these two on purpose. A recommender that asks for a knob on every measurement looks thorough and gets left on the defaults. Two choices per chart, set once when you know the style, are enough for a person to maintain across a catalog.
A concrete pass through one chart
Say the garment chart lists chest circumference, and M is 96 cm with a regular fit and no stretch. The recommender does not treat 96 cm of cloth as a 96 cm body. It subtracts the room a regular cut is supposed to have, and matches the shopper to what is left.
Turn stretch up and that M effectively covers a larger body, so someone who was between M and L on the rigid version can land on M.
Set the same chart to oversized and the aim reverses: the design wants leftover room, so the recommendation moves toward the larger size. The hoodie and the shirt stop sharing a size just because they share a column of numbers.
If your chart already decides the row from a height range (“165–170 cm M”), that column stays in charge. Fit and stretch do not override a height row you meant to be the rule. Use them on charts where chest, waist, or hip is what picks the size.
The body-versus-garment choice itself, and how to measure either one, is in How to make a clothing Size Chart. Set that before you touch fit and stretch. A garment chart mislabeled as body measurements will be wrong no matter how carefully you set the two fields.
What to fill in, in practice
For each garment chart:
- Confirm the chart type is garment, and whether you measured flat or around.
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Set fit intent to the cut you designed, not the cut you wish the factory had made. If the hoodie is oversized, say oversized.
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Set stretch from the fabric, not from hope. A rigid woven is 0. A jersey you can pull on without a zipper is not 0. The control runs 0–20%.
- Publish, then try Estimate my size on one product in that chart and one in a different fit. The two recommendations should disagree when the garments disagree.
Shoppers who estimated from height and weight are using the same matcher as shoppers who typed a tape measurement. Stretch and fit intent apply to both. The estimate’s own uncertainty is a separate thing, covered in Estimate a size without a tape measure.
Where this will not save a bad chart
These fields adjust a recommendation. They do not invent measurements you never entered. A chart with one size, a chart whose rows jump 2 cm then 8 cm, or a chart assigned to the wrong category will still miss. Fix the table first.
They also do not answer “will it suit me?” A roomy hoodie in the right size can still look wrong on the person. That is Virtual Try-On, and it can stay off while you get the numeric answer right. The Size Chart and the recommendation show on the product page either way, which we spelled out in Size Chart without Virtual Try-On.
Install AI Frame on the Shopify App Store. Open a garment Size Chart, set fit and stretch, and check two products before you turn it on for the whole catalog.
