Stop converting sizes and start publishing measurements. Measure your actual garment flat, in centimetres, then convert to inches using the exact factor 2.54 cm = 1 inch. Label every number as garment measurement or body measurement, because they are not the same. There is no universal UK-to-US size standard: each manufacturer sets its own fit, so your chart is the source of truth.
Why a UK-to-US size conversion chart usually fails
Shoppers search for a "UK US size chart" expecting a fixed rule. There isn't one. A UK 12 is not legally or universally a US 8; brands cut patterns differently, and a relaxed-fit jacket in size M can measure wider than a slim-fit L from another label. Conversion tables that map letters and numbers across countries are guesses dressed as facts.
What you can publish honestly is measurement data: the actual dimensions of the item you are selling, plus a clear note on how you measured it. That is more useful than any conversion grid, and it aligns with Google's guidance on helpful content, which asks whether a page provides a substantial, complete description of its topic (Creating helpful, reliable, people-first content).
Garment measurements vs body measurements
These are two different datasets and mixing them is the most common error.
- Garment measurements describe the item itself: chest width across the front, total length, sleeve length, waistband relaxed and stretched.
- Body measurements describe the shopper: bust, waist, hip, inseam, height.
A chart that says "Chest: 96 cm" without saying whether that is the wearer's chest or the shirt's circumference is unusable. State which one you mean, every time.
How do I measure a garment to build the chart?
Measure the item flat, on a hard surface, with a soft tape, and record everything in centimetres first. Centimetres give you finer resolution; you can round inches afterwards.
- Lay the garment flat and smooth it. Don't stretch ribbing or elastic unless you are recording a stretched value separately.
- Measure chest width from one underarm seam to the other, straight across. This is a half-measurement, not the full circumference. Say so in the chart.
- Measure body length from the highest point of the shoulder (or the collar seam, and state which) down to the hem.
- Measure sleeve length from the shoulder seam to the cuff edge, or from centre back if that is how your supplier measures. Pick one method and keep it.
- Measure waist relaxed and fully stretched for anything elasticated. Two numbers, two labels.
- Repeat on three units per size and record the range if it varies. Production tolerance is real.
Write down your method in one sentence under the chart, for example: "Measured flat, chest is the width across the front, not the full circumference." That sentence prevents most returns.
How do I convert cm to inches without guessing?
The conversion is exact: 1 inch = 2.54 cm. To go from centimetres to inches, divide by 2.54. To go from inches to centimetres, multiply by 2.54.
Worked example (hypothetical figures, for illustration only): a shirt measures 52 cm across the chest. 52 ÷ 2.54 = 20.5 inches, so you publish "Chest width (flat): 52 cm / 20.5 in". If you prefer to round to the nearest half inch, 20.5 in is already there. Do not round the centimetre value to a whole number before converting, or you introduce error.
Do the division once in a spreadsheet column and paste the results. Never eyeball a conversion, and never copy a conversion table from another site, because their rounding and their measuring method may differ from yours.
What should the published chart actually contain?
A working chart has four parts:
- Size label as you sell it (UK 10, US 6, S/M/L — whatever your product uses).
- Garment measurements in cm and inches, with the measurement method stated.
- Suggested body measurements if you offer them, clearly separated and labelled as a guide, not a guarantee.
- Fit note: "relaxed through the body", "runs small at the shoulder", "model is 175 cm wearing M".
If you sell into both the UK and the US, keep one chart and label the size column honestly rather than building two pages that drift apart. A single source of truth is easier to maintain and easier for shoppers to trust.
A decision table for tricky items
| Situation | What to publish |
|---|---|
| Stretch fabric | Relaxed and stretched waist/hip, both labelled |
| Oversized fit | Garment measurements plus a fit note |
| Unisex style | Body measurements plus a note that it is cut straight |
| Shoes | Internal length in cm and the brand's own size label |
| No measurement possible | Say so and link to a returns policy instead of guessing |
Where do size charts go wrong most often?
The recurring mistakes are predictable:
- Publishing a conversion table with no garment data.
- Mixing body and garment numbers in one column.
- Stating circumference when the measurement is a flat width.
- Rounding inches from an already-rounded centimetre figure.
- Letting the chart drift out of date after a supplier change.
Build a simple check into your product upload: every new item gets three flat measurements before it goes live. If you use an assistant or a document-based workflow to keep product data consistent, the same discipline of clean source files applies — the output is only as good as the input you control.
How do you know the chart is working?
You cannot promise fewer returns, but you can watch the signal. Track which product pages generate size-related questions and which sizes come back most often. If one size is returned repeatedly, re-measure that size rather than rewriting the copy. Over a few months, a chart built on real measurements gives you a defensible answer to the question every shopper asks: "Will this fit me?"
Follow-up questions
Should I show UK and US sizes side by side?
Only if you label them as your own size labels, not as a universal conversion. A safer approach is to sell in one size system and provide measurements, letting shoppers match those numbers to their own body. If you do show both, add a note that sizing varies by manufacturer.
Do I need different charts for the UK and US markets?
Usually no. Measurements are measurements. What changes is the size label shoppers expect to see, and any local returns wording. Keep one measurement dataset and adapt the label and policy text per market rather than maintaining two charts that can disagree.
