How to choose · Fashion and apparel
How to choose the right clothing size when buying online
Last updated 25 October 2026 · 2 sources listed · Reading time about 4 minutes
Short answer
Ignore the label letter and compare your own body or a well-fitting garment against the retailer's measurement chart for that specific item. Brands and even product lines cut differently, and fabric stretch changes how a number translates to wear. Read the fit notes, model information and customer fit feedback, and check the returns terms before you buy so an imperfect guess costs little.
Who this is for: A shopper ordering garments they cannot try on, who is tired of ordering several sizes and returning most of them.
What to evaluate
Your own measurements
Size labels are not standardised between brands or markets, so only a measurement taken the same way as the retailer's can be compared.
How to check: Measure with a soft tape over light clothing at the fullest chest or bust, natural waist, hips and inseam, and note the retailer's instructions.
A garment that already fits
Laying a favourite item flat and measuring it gives a more reliable guide than an abstract chart, especially for trousers and shirts.
How to check: Compare its flat measurements with the product page's garment dimensions when provided.
Item-specific size chart
Fit varies by style, fabric and country of origin, and a chart for one product line may not apply to another.
How to check: Use the chart on the product page, not a generic one from the shop's help section.
Fabric behaviour
Stretch, drape and shrinkage change fit. A rigid woven fabric forgives less than a knit with elastic content.
How to check: Look at composition and care instructions, and plan for how the fabric will relax or shrink after washing.
Fit description and model details
Phrases such as relaxed, slim or cropped and the height and size worn by the model show intended silhouette.
How to check: Compare the model's stated height and worn size against yours to judge length and proportion.
Customer fit feedback
Reviewers often reveal whether an item runs small, large, short or narrow in shoulders.
How to check: Filter reviews for people with similar build and look for repeated comments about fit.
Returns and exchange terms
Free or easy exchanges lower the cost of guessing wrong, while restrictive terms raise it.
How to check: Check the window, condition requirements and who pays return postage before purchasing.
Comparison
| Method | Good when | Watch out for |
|---|---|---|
| Retailer size chart | Product page provides chart specific to the item with clear measuring instructions | Generic charts that do not reflect that style's cut |
| Measuring a favourite garment | Replacing a staple like jeans or a jacket that you know fits | Garments stretched or shrunk with wear can mislead |
| Fit finder tools | The retailer asks height, build and past purchases to suggest sizes | Recommendations rely on limited data and may not suit unusual proportions |
| Reading reviews for fit | Many reviewers share height, weight and size purchased | Self-reported details are subjective and fashions of fit differ |
| Ordering two sizes and returning one | Returns are free and quick, and the item is important | Environmental and handling cost, and policies that penalise frequent returners |
Decision worksheet
Rate up to three options against this guide’s own criteria. It runs in your browser and saves only on this device. It is a thinking aid, not a recommendation.
1. Have you checked each criterion?
0 of 7 criteria checked.
2. Compare options (0 = fails or unknown, 3 = meets it well)
| Criterion | |||
|---|---|---|---|
| Your own measurements | |||
| A garment that already fits | |||
| Item-specific size chart | |||
| Fabric behaviour | |||
| Fit description and model details | |||
| Customer fit feedback | |||
| Returns and exchange terms | |||
| Total (max 21) | 0 | 0 | 0 |
Questions to ask before you commit
- Does the product page give garment measurements as well as body size guidance?
- Is this item cut true to the label, or described as running large or small?
- What fibres is it made from, and does the care label warn of shrinkage?
- How tall is the model and which size is she or he wearing?
- What is the return window and are there conditions such as unworn with tags attached?
- Who pays return carriage, and how fast is the refund processed?
- Is the item final sale, or excluded from returns for hygiene reasons?
Typical trade-offs
Size up for comfort
- Upside
- Easier movement and room for shrinkage in natural fibres.
- Downside
- Looser shoulders, sleeves and lengths that may look sloppy.
Order the closest measurement match
- Upside
- Better silhouette as designed.
- Downside
- Little tolerance for fabric shrinkage or weight change.
Use a retailer fit tool
- Upside
- Quick suggestion for unfamiliar brands.
- Downside
- Depends on how well the data fits your body type.
Buy from sellers with generous returns
- Upside
- Low risk when trying sizes.
- Downside
- Prices or restrictions may compensate, and frequent returns can cause account limits.
Common mistakes
- Trusting the letter on the label. Compare measurements, since a medium in one brand may equal a small or large in another.
- Measuring over bulky clothing or pulling the tape tight. Use a relaxed, level tape and ask someone to help with back measurements.
- Ignoring fabric. A shirt in a rigid cotton and one in stretch jersey share a size but fit differently.
- Forgetting length. Check inseam, sleeve and hem measurements, especially if you are much taller or shorter than average.
- Washing before checking fit. Many retailers require unworn, unwashed items for returns, so try on indoors first.
Related questions
Why do sizes differ so much between brands?
There is no single binding standard for how brands translate body measurements into labels. Each company draws up its own fit patterns based on target customers, design aims and production history, and regional conventions add further variation. Vanity sizing, where labels are made flattering, complicates comparison. The reliable approach is to compare your measurements with the garment-specific chart rather than the label.
How do I measure myself accurately?
Stand relaxed with feet together and wear light clothing. Keep the tape level and snug but not tight around the fullest part of the chest or bust, the natural waist and the widest part of the hips. For inseam, measure from the crotch to the ankle on a trouser that fits. Re-measure for confirmation, and follow the retailer's own instructions where they differ.
Should I size up when buying natural fabrics?
Cotton, linen and wool may shrink or relax with washing depending on how they are processed, so if the item is not pre-shrunk or the care label says so, a little extra room can be wise. Knitted fabrics can stretch out with wear. Check the product description and reviews for statements about shrinkage rather than assuming, and follow the care instructions.
Do fit finder tools work?
They can be helpful starting points, particularly for brands with large histories of purchase and return data, but their quality depends on data and on how closely you match typical patterns. Use them alongside the size chart and reviews. If suggestions conflict with your measurements, trust the measurements for that product.
Are there items I should not buy without trying on?
Closely fitted pieces such as tailoring, jeans, swimwear and shoes tend to carry higher fit risk, as do items from unfamiliar brands. For those, favour sellers with straightforward returns and use the brand's own measurements. Loose knitwear, accessories and stretchy basics usually tolerate size variation better.
Sources and further reading
These pages were reachable when we last checked. They informed definitions and rules referred to above; they do not endorse this guide. Where rules differ by country, check the authority for your location.
- Business Guidance — Federal Trade Commission, retrieved 27 October 2026
- Consumer protection rights — GOV.UK, retrieved 27 October 2026
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