The shop says it stocks your size. Here is how to check before you get there.

The rail stops at an 18. It always stops somewhere, and the assistant is already saying the sentence — we can order that in for you — with the particular brightness of someone who has said it four times today. The website said the shop had it. The website was not lying, exactly. It was answering a different question from the one you asked.

Range and allocation are two decisions made by two departments. Range is what a brand has designed and graded: the sizes that exist as patterns, as fabric orders, as barcodes. Allocation is what gets sent to a building with a door on it. A chain can carry sizes up to a 28 in the truest sense — they are made, photographed, sitting on a shelf in a distribution centre — and send none of them to the branch nearest you, because the buying team looked at last season’s sell-through in that postcode and decided the space was worth more to a 12.

Which means the question worth asking is never whether a shop stocks your size. It is whether this shop, today, has units of that size on the floor. Here is how to find that out without leaving the house.

Use the store stock checker, and know what it is not telling you

Most large retailers have one, usually behind a small link on the product page: check availability in store, find in store, something similar. Put in your postcode and it returns a list of branches with a traffic light against each size. It is the single most useful thing on the site and almost nobody uses it, partly because it is buried and partly because it is often wrong in one specific, predictable way.

What it reads is the stock ledger, not the shop floor. A unit that is in the building but still in a cage in the stockroom shows as available. A unit that has been carried to a fitting room, abandoned on the wrong rail and not rescanned for a fortnight also shows as available. Green means somewhere on the premises. It does not mean findable in ten minutes by you.

So read the number, not the colour, where the site gives you one. Low stock against your size, in a shop that carries the range properly, usually means one or two units and one of them is on a mannequin. Three or more is a rail.

The filter lies by omission on the listing page

Filter a listing page by size and you get every product that exists in that size anywhere in the company. It is a catalogue query. It has no idea where you are and no opinion about what is in your nearest branch, and it will cheerfully show you four hundred items of which the shop down the road holds nine.

The tell is the product page itself. Open three or four items from that filtered list and look at whether the size is available for click-and-collect at your branch, not just for delivery. A retailer that will send a size to a store for you to collect is a retailer that holds it centrally; a retailer that offers it for home delivery only is often one that has it in a third-party warehouse and has never put it in a shop at all.

If you ring, ask a question with a number in it

Do you stock plus sizes gets you a yes, because the honest answer to that question is yes somewhere. Ask instead: how many units of the black wool coat in a 24 are on the floor right now, and can you put one behind the till for an hour. Both halves matter. The first forces someone to look at a screen or a rail. The second tells you whether the shop takes the sale seriously enough to hold it, which is its own piece of information.

Staff will almost always do this. It is a normal retail request that has somehow acquired the status of an imposition, and the worst outcome is a no that costs you nothing.

Click and collect is the reliable version of the trip

It is the only way to get the warehouse’s stock into a fitting room without paying for the privilege. You order the size, the shop receives it, you try it there, and you hand back what does not work at the counter rather than repackaging it and queueing at a parcel shop. Order two sizes if the item is between grades; the second one costs nothing if you return it in person.

The catch is the collection window, which is usually a week and occasionally five days. Diary it. An uncollected order goes back into stock and the refund takes its own sweet time.

What the return policy tells you about the range

A brand that puts its extended sizes online only, charges for returns, and excludes them from in-store returns has made a decision about who absorbs the cost of an uncertain fit. That is not a moral failing on their part, it is an allocation model, but it is worth pricing in before you order four things intending to keep one.

It is also a reasonable predictor of longevity. Ranges that never make it into a physical shop are the ranges with no floor sales to defend them at the next review, which is a large part of why an extended range can be launched to a great deal of noise and quietly thin out eighteen months later without any announcement at all.

Two habits that save more time than any of this

Read the brand’s own measurement chart rather than the letter or the number, once, for the brands you actually buy. Write the three numbers that matter for your body on a note on your phone. Sizing is not standardised between companies and never has been; the chart is the only thing in the transaction that is measured in centimetres and therefore the only thing that means anything.

And when something fits properly, buy the second one. Not as a treat — as insurance. The range it came from may not be there in a year, and the specific cut that worked almost certainly will not be.