When you fall between two sizes

Short answer: Choose the smaller of two sizes for knitted styles with stretch and the larger for woven styles without stretch. Bamboo viscose follows the body well, so the smaller size usually fits right when elastane is part of the fabric.

Knit gives way, woven fabric does not

A knitted garment with elastane in the yarn adapts to the body and gives a couple of centimetres, whichever of two neighbouring sizes you pick from the label. A woven fabric does not do the same, so the larger of the two sizes is usually the right choice there instead. See bamboo t-shirt for women.

Underwear needs to fit close to work well

Underwear that is too large rolls up and creeps up or down over the course of the day, because there is not enough tension to keep the fabric in place against the skin. Choose the smaller of two sizes, then, whenever the fabric has stretch built into it. See bamboo panties.

Measure instead of guessing

Measure waist and hip with an ordinary tape measure, and check the numbers against the brand's own size chart, not against a size you normally wear elsewhere. Sizes vary considerably between brands, even when they use the same letter or the same number on the label to describe them. See bamboo underwear for women.

The fabric's stretch decides how far you can size down

The more elastane a knitted fabric contains, the more confidently you can choose a smaller size without the garment feeling uncomfortably tight against the body. A fabric with no elastane at all, even if it is knitted, behaves more like a woven fabric and should be sized up rather than down.

Body shape matters more than weight alone

Two people with the same weight can need different sizes, because how the body carries that weight affects where a garment feels tight or loose first. Always measure the exact spot where the garment needs to fit close, rather than estimating from weight or a usual off the shelf size.

Seasonal fabric can change how a garment fits

A thicker autumn or winter garment in the same size can fit tighter than a thin summer garment, because the fabric layer itself takes up more room under the arms and across the hips. Always check the item's own fit description when one is given, rather than relying only on past experience.

Try the garment on if you are unsure

Order two sizes if you are torn between two neighbouring sizes, and return whichever one does not fit well. This is a far more reliable method than guessing from numbers alone, especially on a first order from a brand whose fit you do not already know well.

Washing can change how a garment fits over time

A garment that fits just right at purchase can feel tighter after a few washes if the elastane is not treated gently from the start. Follow the care instructions from day one to keep the fit as close to original as possible, and avoid unnecessary shrinkage along the way.

How to remember the rule going forward

Size down for knit with stretch, size up for woven without stretch. Measure yourself rather than guessing, and always check the numbers against the specific brand you are ordering from, rather than a general sense of your own usual size across different shops.

Frequently asked questions

Should I size up or down between two sizes?

Down for knitted styles with stretch in the yarn, up for woven styles without stretch, where the fabric itself does not give way to the body's movement.