You order your usual size. It arrives. The shoulders are fine but the sleeves are short, or the waist fits and the hips don't, and the whole thing goes back in the bag. Repeat that a few times and online shopping starts to feel like a lottery you keep losing.
It isn't a lottery. Sizes are marketing; measurements are facts. The moment you stop shopping by size letter and start matching your numbers to the garment's numbers, most of the guesswork disappears. A size 10 means nothing consistent across brands, countries, or even two ranges from the same label — but 96 cm across the bust means exactly one thing everywhere.
Here is the checklist to run before you press buy, in the order that catches the most mistakes soonest.
Step 1: Take your five numbers once
This is a twenty-minute job you do once a year, and it does more for your hit rate than every other tip combined. Use a soft tape, wear thin clothing, and keep the tape level rather than tight.
- Bust or chest — around the fullest part, tape level under the arms.
- Natural waist — the narrowest part of your torso, usually just above the navel. Bend sideways; the crease is your natural waist.
- Hips — around the fullest part of the seat, usually several inches below the waist.
- Inseam — from the crotch seam to where you want the hem, measured on a pair of trousers that already fit rather than on your leg.
- Shoulder to shoulder — across the back, from the bony point of one shoulder to the other.
Two more are worth adding if you buy a lot of shirts or jackets: sleeve length (shoulder point to wrist bone, arm slightly bent) and rise (crotch seam to top of waistband on trousers that fit).
Save them in your phone's notes app in both centimetres and inches. Every checklist step below refers back to them.
Step 2: Find the garment measurements, not just the size chart
This is the single most misunderstood part of online shopping, and it's where most returns are born.
Retailers publish two very different kinds of table:
- A body size chart says "size M fits a 96–101 cm chest." That is a claim about you.
- Garment or flat measurements say "size M measures 108 cm around the chest, laid flat and doubled." That is a fact about the item.
The gap between the two is ease — the deliberate extra room the designer added so the thing can be worn and moved in. A tailored shirt might carry a little; an oversized coat carries a lot. Two garments with identical body-size charts can differ by a hand's width in actual circumference, which is exactly why the same "M" fits differently on two tabs of the same browser.
The rule: if flat measurements are published, use them and ignore the size letter. If only a body chart exists, treat your order as an experiment and check the returns policy before committing.
When flat measurements are given, compare them against a garment you already own and love rather than against your body. Lay your favourite shirt flat, measure chest, length, shoulder, and sleeve, and use those as the target. You are no longer guessing at ease — you are copying a fit you already know works.
Step 3: Read the fibre content before the styling photos
Fabric decides how much your measurements are allowed to be wrong.
A rigid woven cotton or linen has almost no give: if the flat measurement is smaller than your body measurement, it will not fit, full stop. A knit, or a woven with a few per cent elastane, tolerates a mismatch and springs back. Heavy fabrics hold their cut; drapey ones follow your shape and reveal more of it.
Two practical consequences:
- On stiff wovens — denim, poplin, linen, most tailoring — size to the largest of your relevant measurements and accept alterations elsewhere.
- On stretch and knits — jersey, rib, ponte, anything with elastane — the flat measurement can sit at or slightly under your body measurement, because it will stretch to meet you. Ordering these a size up is how people end up with shapeless items.
Fibre content also predicts shrinkage, pilling, and how the piece will look after a month. Our guide to reading a fibre label covers what each fibre actually does in wear, which matters as much as the number on the tag.
Step 4: Use the model information as data
Most listing photos are styled on one body, and that body is not a neutral reference — but the caption underneath it usually is.
- "Model is 178 cm and wears a size S" tells you where the hem and sleeve will land relative to your own height. If you are noticeably shorter, a "midi" becomes a maxi and a cropped jacket stops being cropped.
- Photos on more than one body size are a genuinely useful signal, and their absence on a size-inclusive range is worth noticing.
- Watch the back of the photo. If the garment looks miraculously fitted from the front, it may be clipped behind. Look for a side or moving shot, or a customer photo, before you trust the silhouette.
Step 5: Mine the reviews for fit signal only
Ignore the star rating and search the review text for the words runs, sizing, ordered, height, and returned.
What you want is a reviewer who states their measurements or their usual size alongside what they ordered. One person saying "runs small" is noise; five people saying it in the same words is a specification the brand forgot to publish. Pay particular attention to reviews mentioning the specific area you're unsure about — arms, shoulders, thighs, rise — since a garment can run large overall and still be tight in one place.
Step 6: Check the parts a tailor can't rescue
Some fit problems are cheap to fix, so a near-miss is still a good buy. Others make the item a write-off no matter how well the rest fits.
- Fixable, cheaply: hem length, sleeve length on casual pieces, taking in the waist and side seams, tapering a trouser leg.
- Not worth fixing, or impossible: the shoulder line on a structured jacket, the rise of trousers, the shape of an armhole, and anything that needs letting out when there's no seam allowance inside.
So when you're deciding between two sizes, size for the un-alterable parts and let the tailor handle the rest. The full breakdown is in our guide to which alterations are worth a tailor.
Step 7: Price the return before you buy
The returns policy is part of the cost of the item, and it varies far more than the product pages suggest. Before checkout, confirm four things: whether return postage is paid or deducted, how long the window is, whether the item is marked final sale, and — for cross-border orders — whether duties and taxes are refunded. A cheaper item with a paid return can easily be the more expensive purchase.
This also decides your ordering strategy. Order two sizes only where returns are free and easy and the fit is genuinely borderline. Order one size where returns cost money — and put the effort into steps 2 and 3 instead.
A worked example: buying a blazer online
You want a wool blazer. Run it in order:
- Your numbers: chest 100 cm, shoulder 44 cm, sleeve 62 cm.
- Garment measurements: the size M lists chest 108 cm flat-doubled, shoulder 45 cm, sleeve 63 cm. The 8 cm of ease over your chest is normal for a tailored jacket worn over a shirt. Shoulder and sleeve are within a centimetre. Good match.
- Fabric: 100% wool, no stretch. So the chest measurement has to be right at purchase — it will not give.
- Model note: model is taller than you, so the body length will sit slightly lower on you than pictured. Acceptable on a blazer; it would be decisive on a cropped jacket.
- Reviews: three mention "sleeves run long". Sleeves are on the cheap-to-fix list, so this is a non-issue.
- Un-alterable check: shoulder is the only structural number, and it matches. Buy it.
Reverse that — shoulder 3 cm too wide, sleeves perfect — and it's a return, because you'd be paying for the one alteration that isn't worth making.
Step 8: The ten-minute test before you cut the tags
When the parcel lands, keep the tags on and do this:
Put it on over the layer you'd actually wear it with. Sit down. Raise both arms overhead. Reach forward as if for a steering wheel. Do up every button and look at the button band for horizontal pulling. Check the shoulder seam sits on your shoulder bone. Then look at the construction — seams, buttonholes, pattern matching — using the same checks as our guide to telling whether clothing is good quality, because a good fit in a badly made piece is a short-lived pleasure.
If it fails the sitting or reaching test, it goes back. Clothes that only work standing still are clothes you won't wear.
FAQ
Should I order two sizes and return one? Only when returns are free and the fit is genuinely borderline. It's a legitimate tactic, not a moral failing — but it's expensive where postage is deducted, and it's a habit that hides the real fix, which is knowing your measurements.
What if the retailer only publishes a body size chart? Compare it to your numbers, then read reviews specifically for "runs small / runs large" and check the fabric for stretch. Where all three point the same way, order accordingly. Where they conflict, treat it as a high-risk order and buy only if the return is free.
Why does the same size fit differently across brands? Because there's no enforced standard. Every brand cuts to its own fit model and its own house amount of ease, and ranges within one brand often differ too. This is precisely why flat measurements beat size letters.
Between two sizes, which do I pick? Size for the part that can't be altered — shoulders on structured jackets, rise and hip on trousers, chest on rigid wovens — and plan a cheap alteration for the rest. On stretch knits, size to the smaller number; on stiff wovens, size to the larger.
Do vanity sizing and international conversions matter? Enough to be careful. Conversion charts between UK, US, EU and Asian sizing are approximations, not equivalences, and labelled sizes drift over time. Measurements don't convert or drift — one more reason to shop by the numbers.
The takeaway
Online fit stops being a gamble the moment you shop with data: five measurements of your own, the garment's flat measurements, the fibre content, and a clear head about which flaws a tailor can fix. Take the numbers once, keep them in your phone, and the checklist takes ninety seconds per order.
When you know your numbers and what you're looking for, see where to buy wardrobe essentials on FashionTV24 and shop the pieces that will still fit next season.
