A familiar size on a label is a starting point, not a fit guarantee. Before buying, compare the seller's actual garment measurements with a similar item you already wear comfortably. Use the same measurement points, the same units and the same relaxed or stretched state.
This guide helps you make that comparison without turning a size label into a promise. You do not need to send a stranger photographs of your body or personal body measurements.
Start with the item you already own
Choose a reference garment with the fit you want. Compare jeans with jeans of a similar rise, and a fitted shirt with another fitted shirt. For a jacket, choose a reference jacket that fits comfortably over the layer you intend to wear underneath. A loose T-shirt is not a useful size template for a tailored blazer.
Lay the reference item flat, smooth it gently and fasten it as you would wear it. Do not pull stretchy fabric tight unless you are deliberately recording a separate stretched measurement. Ask the seller to measure the item for sale in the same way. A photograph showing the tape's start and finish is more useful than a number without context.
Levi's SecondHand sizing guide explains why cut, era and fabric can make a jeans tag unreliable and why its resale programme records actual measurements. That does not make its size chart a universal conversion for other brands.
Make a like-for-like comparison
| Item | Useful garment measurements | What to clarify |
|---|---|---|
| Jeans or trousers | Relaxed waistband width, inside-leg length, front rise | Where the waistband sits; stretch; hems or waist altered |
| Shirt or T-shirt | Underarm-to-underarm width, shoulder width, length | Exact length starting point; slim or relaxed shape |
| Dress | Underarm width, waist position/width, length | Fitted or elasticated areas; lining; where length was measured |
| Jacket | Underarm width, shoulder width, sleeve and body length | Whether measured fastened; space for your intended layer |
For trousers, the inside-leg length runs along the inside seam from the crotch seam junction to the hem. Front rise runs along the front from that junction to the top of the waistband. Ask for photographs of the tape placement if either starting point is unclear.
Write down “my item” and “seller's item” side by side. Identify the dimension that would actually stop you wearing it: a short inseam, tight upper arm or waist that sits in the wrong place. Matching one number does not resolve the others.
Flat width is not body circumference
A seller saying “waist 40 cm” may mean the waistband measured across the front while lying flat. That is not a 40 cm measurement all the way around. Doubling a flat width can give a rough garment circumference, but curved waistbands, fabric stretch and measuring technique make it an approximation—not an exact body-fit calculation.
The simplest comparison is flat garment width against flat garment width. Do not compare an unstretched clothing width with a body circumference or mix centimetres and inches.
A worked example: two pairs both labelled the same size
Imagine your comfortable jeans measure 39 cm across the relaxed waistband with a 76 cm inside leg. The seller's jeans measure 37 cm across and 70 cm inside leg. Those are illustrative numbers, not a sizing recommendation.
Even if both tags show the same size, the offered pair is narrower and shorter by this measuring method. A seller saying “they stretch” does not establish whether you will like the fit. Ask about the fabric label, rise and any alterations; if the comparison still does not work, pass on the pair.
Send one useful message
Suggested message—not a customer quote:
Hi! Could you measure the waistband across while the jeans are laid flat and relaxed, plus the inside leg and front rise, in centimetres? A photo with the tape would help. Have the waist or hems been altered, and is the fabric stretchy? I'm comparing them with a pair that fits me.
For another garment, replace those measurements with the relevant row above. Read the listing first so you only ask for missing information.
When to wait rather than buy
Wait when a seller cannot explain what was measured, gives contradictory numbers, or cannot confirm a dimension that matters to you. A discount does not make a garment longer. Nor should you assume a change-of-mind return will solve an uncertain fit: check the applicable terms before paying.
If the fit comparison works, move on to the condition of the actual item. Fit and condition are separate decisions.