For this LAUMA model, size 29–31 refers to the circumference of the calf in centimetres. Measure the widest part of your lower leg, ideally in the morning when swelling is usually lower. If your measurement falls within 29–31 cm, this is the intended size range for this product.
Fit matters more with compression knee-highs than with ordinary socks. The fabric is designed to apply graduated pressure: strongest at the ankle and gradually lighter toward the knee. If the sock is too loose, that pressure gradient may not work as intended. If it is too tight, especially at the top band, it can dig into the skin or create uncomfortable pressure.
After putting them on, check that the sock sits smoothly from ankle to below the knee, without wrinkles, rolled edges or tight folds. Wrinkles can create uneven pressure points, while a rolled top band can feel restrictive. The knee-high should feel supportive and firm, but not painful, and your toes and foot should not feel numb, cold or unusually uncomfortable.
If you are between sizes, have one leg noticeably more swollen than the other, or have been advised to wear a specific compression class, it is best to ask a pharmacist or doctor before choosing. This is especially important if you have diagnosed venous insufficiency, diabetes, peripheral arterial disease, skin infections or open wounds on the legs.