Why a medium isn't the same size at every brand

A medium is a name each brand fills with its own measurements. Nothing ties one brand's M to another's: each one chooses the body its M is made for, how much room the garment leaves around it, and how much it grows from one size to the next. Two Ms can share a letter and miss each other by a full size.

That is not a fault to fix across the industry. It is a fact a store can work with, by publishing what its own M measures.

Same letter, different numbers

You don't need to compare brands to see it. Here is the M of seven templates inside one app, Ruban Size, all in body measurements:

Seven Ms, five different bodies. Each is reasonable for its product. Different brands do the same, each with numbers of its own.

Three reasons a medium moves

Grading: how sizes step

A size range is built by grading: start from one size and add or take away a set amount for each size up or down. How much is the brand's choice, and it can change along the range.

In the women's tops template, the chest grows by 5 cm from XS to S and by 7.5 cm from L to XL (center to center). In the scrubs template it grows by 7 cm from XS to S, then 8 cm a size. Two ranges that start close can be a size apart by XL.

Fit intent: how much room

The same body can need a different size depending on how the garment is meant to sit. The templates' fit notes say it in a line:

• Cycling and compression wear: "Very close fit: for a relaxed ride, take one size up."
• Leggings and activewear: "Compression fit: if you prefer less support, take one size up."
• Coats and jackets: "Cut to layer: for a closer fit, take one size down."

A compression legging is meant to be smaller than the body; a coat is meant to go over a sweater. How much ease clothes need gives the numbers by garment. Fit intent is why the same brand can have an M that runs small and an M that runs large.

Target customer: whose body

A brand cuts its M for the people it sells to. A unisex scrubs M has a chest of 95 to 102 cm; a women's top M, 90 to 95 cm. A petite M has the same girths as a regular M with shorter lengths. Neither is wrong; they are made for different bodies.

Then there are the labels themselves. Some brands give the same body a smaller number to flatter it, which vanity sizing explains.

One shopper, three answers

Take one shopper: a 94 cm chest, a 76 cm waist and 102 cm hips. Here is where each measurement falls, and what Find my size answers on three of the templates:

On the leggings and the scrubs, the answer also carries a line about the fit scale: "This item runs small: we took it into account." on one, "This item runs large: we took it into account." on the other.

Same body, three sizes, and every one of them right for its product. A shopper who orders "my usual M" gets one of three. Try the leggings with those measurements:

The fix: publish your measurements and a fit note

You can't make other brands agree with you. You can make your own sizes readable:

1. Publish your own numbers. Measure your garments, or take the body measurements your patterns are made for. Ruban Size's templates start with typical values and say so: "Typical values: adjust them to your brand's own measurements before publishing."
2. One chart per fit. Leggings and tops are cut differently, so they get different charts, even when the letters match.
3. Set the fit scale and a note on every chart where the cut doesn't follow the chart (see what "true to size" means).
4. Let shoppers compare their body with your numbers, not with another brand's M.

How Ruban Size handles it

Your numbers, quickly. Paste your chart from Excel, Numbers or Google Sheets, or start from the women's tops template and replace the values. Coming from another app, the import (Pro) recreates your charts from Kiwi, MP, BF or ESC with the products they show on, and the AI import (Pro too) reads a photo, a PDF or a web page into a draft you check.

The right chart on each product. Rules assign charts by tag, type, vendor, collection, words in the title or SKU, so leggings get the leggings chart and tops the tops chart. The product rules page shows how, with the products listed before you save.

Fit, chart by chart. In the editor's Fit and Find my size tab, each chart gets its five-step fit scale and its note. The leggings template comes set one step small, coats one step large.

A size from the shopper's body. Find my size compares the shopper's measurements with the chart on that product, then applies its fit scale. The measurements stay on the shopper's device, and "Your size" is worked out again from each product's own chart. That same shopper sees "Your size: M" on your tops and "Your size: L" on your leggings, without knowing anything about how you grade.

Questions

Why am I a medium in one brand and a large in another?

Each brand decides which body its M is made for, how much room it leaves, and how sizes step up. Check the measurements in each brand's chart rather than the letter.

Should I copy another brand's size chart?

No. Their chart describes their garments. Copy it and your M carries their measurements on a cut that may be different, which is the mismatch you were trying to avoid.

How do I keep sizes consistent across my own products?

Use the same measurements for products cut from the same pattern, give different cuts their own charts, and mark the exceptions with a fit scale and a note.

Does Find my size know how other brands size?

No, and it doesn't need to. It compares the shopper's measurements with the chart on your product page, adjusted by that chart's fit scale, so the answer is about your M.