You should size up when a garment is structured, non-stretch, fitted, layered or your measurements sit near the top of the size range.
High-level answer
Do not size up or down by habit. Decide based on the garment type, fabric, fit description and your measurements.
High-level answer
You should size up when the garment is structured, non-stretch, fitted, layered or your measurements sit near the top of the size range. You should size down when the garment is oversized, stretchy, relaxed or your measurements sit near the bottom of the size range.
The safest rule is simple: do not size up or down by habit. Decide based on the garment type, fabric, fit description and your measurements.
The better question: where are you between sizes?
Most sizing mistakes happen when shoppers treat size labels as fixed. They are not. The real issue is whether your measurements sit closer to the lower or upper end of a brand’s size range.
If your waist, hips or chest are near the top of a size range, the next size may fit better. If they sit near the bottom, the smaller size may work, especially in relaxed or stretchy clothing.
When to size up
Size up for structured clothing
Blazers, shirts, coats and tailored trousers usually have less give. If your chest, shoulders, waist or hips are at the upper end of the range, sizing up can prevent pulling, tight sleeves or restricted movement.
Size up for rigid fabrics
Rigid denim, non-stretch cotton, linen and tailored fabric are less forgiving. A size that technically matches your measurements can still feel tight if the fabric has no stretch.
Size up for fitted silhouettes
Bodycon dresses, slim shirts, skinny jeans and fitted jackets leave less room for measurement error. If you are between sizes, the larger size is often more comfortable.
Size up for layering
Outerwear should allow room for what you wear underneath. A jacket that fits over a T-shirt may feel too tight over knitwear.
When to size down
Size down for oversized fits
If a product is deliberately oversized, your normal size may already include extra room. Sizing up can make the garment look too large rather than relaxed.
Size down for stretch fabrics
Stretch denim, jersey, ribbed knits and elastane blends can adapt to the body. If your measurements are near the lower end of the range, the smaller size may give a cleaner fit.
Size down if you prefer a closer fit
Fit preference matters. Two people with the same measurements may choose different sizes because one wants ease and the other wants shape.
Category-by-category rule
Jeans
Use waist, hips and inseam. Size up in rigid denim if between sizes.
Dresses
Use bust, waist and hips together. Size for the largest key measurement.
Jackets
Prioritise shoulders, chest and layering room.
Shirts
Check chest, shoulders and sleeve length.
Shoes
Use foot length first, then width and brand fit notes.
Trousers
Compare waist, hips, inseam and rise.
Bottom line
Size up when the garment has less give or your measurements are near the top of the range. Size down when the garment is oversized, stretchy or your measurements are near the lower end.
The best answer comes from your measurements, not from guessing.