Is there a standard for what a size 10 means?
Start with the fact that explains everything else. There is no authority anywhere that decides what a size 10 means, checks that a brand has got it right, or penalises one for disagreeing with another.
Various countries have published sizing standards and recommendations over the years. Following them is voluntary, and a great many brands do not. A label is a claim the brand makes about its own garment, and the only thing making it true is the brand saying so.
Once you accept that, the frustration mostly dissolves. Two shops disagreeing about a size 10 are not making an error. They never agreed in the first place, and neither of them was ever going to.
What is a fit block, and where does a size come from?
A garment does not begin as a size range. It begins as one sample, cut to fit one specific set of measurements, and that set is called the fit block. You will also see it called a base size or a sloper.
The block is a decision, and it is one of the more consequential decisions a brand makes. It usually reflects who the brand thinks it is selling to: the market it operates in, the age of its customer, and often a body shape the brand has been building on for years because changing it would upset everyone who currently fits.
Everything the brand produces starts from that block. The designer cuts the first pattern to it, the sample is fitted on a model chosen to match it, and the corrections made in fitting are baked back into it. By the time a garment reaches a shop, the block has shaped every measurement on it.
This is why a brand feels consistent with itself and unpredictable against everyone else. You are not learning a size when you learn a brand. You are learning its block.
What is grading, and how does one pattern become a whole range?
The rest of the sizes are made by stepping the base pattern outward and inward, a process called grading. A pattern maker decides how much to add at each size and, more importantly, where to add it.
That second part is where two brands can share a base size and still end up different. Adding width evenly around a garment produces one result. Adding more at the side seam than at the centre front produces another. Adding length as the sizes grow, on the reasoning that larger bodies are often taller, produces a third.
The practical effect is that two brands can agree closely at their base size and diverge noticeably at the ends of the range. If a brand fits you well in the middle of its sizes and badly at the edges, you have run into its grading rather than its block.
How different can one size be between three shops?
Put a body that measures 96 centimetres at the bust into three shops and the size that comes out is a block decision each time, not a single fact about that body.
| Shop's positioning | Block built for | Size a 96cm bust gets |
|---|---|---|
| Fitted, younger market | A smaller base body, close cut | 12 to 14 |
| Standard high street | An average base body for the market | 10 |
| Relaxed, generous fit | A larger base body, roomier cut | 8 |
None of the three shops has made an error. Each one built its range on a block it chose for a reason, and the label is only ever honest about that one shop's own scale. The bust measurement did not change between rows. The block underneath the number did.
Why has the same size number grown over the years?
There is a second effect layered on top of the first, and it works across decades rather than across shops.
The body covered by a given size number has grown over time. A garment from an earlier decade carrying a number will usually fit a smaller person than a current garment carrying the same number. Brands have moved their blocks gradually, and the number on the label stayed put.
This is worth knowing for one specific reason: it makes vintage and secondhand sizing genuinely unreliable, in a way that current sizing only feels unreliable. A label from decades ago is describing a different scale entirely. That case gets its own chapter, because flat measurements are the only way through it.
For shopping new clothes today, drift explains little. Two shops on the same street disagreeing right now is a block difference, and it would exist even if nothing had changed since the day the numbers were invented.
What does runs small actually mean?
Review sections are full of the phrase, and it turns out to be a reasonably precise statement once you know what is behind it.
A garment running small usually means the brand's whole range is shifted by roughly one step against what its customers expected, either because the block is smaller than the market average or because that particular style was cut close. When several reviewers say it independently, they are describing a real offset and ordering one size up corrects it.
Weight it by how many people say it and whether they gave their own numbers. One person saying a garment runs small is reporting a surprise, and a surprise is about their expectation rather than the garment. Six people saying it, two of whom mention their usual size, is data.
What should you carry between shops instead of a size?
Since the number moves and your body does not, the useful thing to carry between shops is something that stays fixed. There are two good candidates and it is worth having both.
The first is your own measurements, taken once and written down. Those go straight into any body chart in any country, and they are the subject of the next chapter.
The second is a reference garment. Pick something you own that fits the way you like, lay it flat, and measure across the chest, across the waist, and from the shoulder seam to the hem. Keep those three numbers with your body measurements.
A reference garment answers a question your body measurements cannot, which is how much room you actually want. Two people with identical chest measurements can want different jackets, and a garment you already love encodes that preference as a number you can compare against a listing.
How do you build your own size note for each brand?
The other thing worth doing takes about a minute per brand and pays for itself immediately.
When a garment from a new brand fits well, write down the brand and the size. When one fits badly, write down the brand, the size and which direction it was wrong in. After a handful of purchases you have a short personal list that beats any general conversion table, because it is built from your body against those specific blocks.
Keep it with the measurements. It survives a brand renumbering its range, since you can always go back to the chart, and it removes the guesswork from repeat purchases entirely.
Which brands are safest to order from without trying on?
Some retailers make this much easier than others, and the signal is simple to read.
A brand that publishes a detailed body chart in centimetres, per size, is committing to a number you can check against yourself. That is worth a great deal, and it usually correlates with the brand caring about fit more generally.
A brand that publishes flat garment measurements per size is being even more useful, because you can compare against your reference garment directly. This is common on menswear and workwear sites and rarer elsewhere.
A brand that publishes only small, medium and large with no numbers attached has told you that it would rather you guessed. Where returns are free that is survivable. Where they are not, it is a reason to buy something else.
Why do two ranges from the same brand fit differently?
Worth knowing because it looks like inconsistency and has a straightforward explanation.
Large retailers often run several ranges at once, and those ranges can sit on different blocks: a main line, a premium line, a younger line, a collaboration. Production also moves between factories, and the same pattern in a different fabric behaves differently.
So one garment from a brand fitting and another not is normal, and it is not a sign you measured wrong. Check whether the two came from the same part of the business before concluding anything about the brand as a whole.